Introduction {#Sec19}
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Child maltreatment is a serious problem that affects many children around the world. A recent series of meta-analyses showed that worldwide prevalence rates of child maltreatment ranged from 0.3% based on studies using maltreatment reports of professionals to 36.6% based on self-report studies (Stoltenborgh et al. [@CR168]). Child maltreatment is associated with serious short-term and long-term negative consequences, such as physical, behavioral, and psychological problems, leading to high costs for individuals and society (Alink et al. [@CR3]; Gilbert et al. [@CR79]; Jonson-Reid et al. [@CR99]) . Given the high prevalence rates and serious consequences of child maltreatment, effective prevention of child maltreatment is essential. The number of interventions aimed at preventing or reducing child maltreatment has grown over the years. However, several meta-analyses on the effectiveness of these interventions showed only a limited effect (e.g., Euser et al. [@CR61]; Geeraerts et al. [@CR76]; MacLeod and Nelson [@CR121]; Sweet and Appelbaum [@CR171]). Therefore, it is very important to unravel intervention components that contribute to intervention effectiveness from components not contributing to (or even negatively affecting) intervention effectiveness. Consequently, new promising interventions may be developed and existing interventions may be improved by integrating effective components in interventions and/or eliminating ineffective components from interventions. To enhance knowledge on how specific components of child maltreatment interventions affect the effectiveness of these interventions, a comprehensive meta-analysis was performed in the present study.

The number of interventions aimed at preventing or reducing child maltreatment has increased exponentially over the last decades (Daro [@CR43]). Most interventions target a clearly defined population that is identified on the basis of risk factors for child maltreatment, such as teenage mothers, drug or alcohol addicted parents, or multiproblem families. Interventions may be aimed at *reducing* the incidence of child maltreatment in maltreating families or at *preventing* the occurrence of child maltreatment in at-risk, but non-maltreating families. The former are often system interventions, whereas the latter often comprise home visitation interventions in which parents are visited at home and provided with information, support, and/or training regarding child health, development, and care. These interventions often begin prenatally and continue during the child's first 2 years of life, but may also begin after birth and last only a few months. In addition, some interventions are aimed at preventing the first occurrence of child maltreatment in the general population, for example by providing a short parental skills training to parents who visit a well-baby clinic.

A number of meta-analyses have synthesized results on the effectiveness of interventions aimed at preventing or reducing child maltreatment (e.g., Euser et al. [@CR61]; Filene et al. [@CR69]; Geeraerts et al. [@CR76]; Guterman [@CR83]; Layzer et al. [@CR110]; Pinquart and Teubert [@CR145]; Sweet and Appelbaum [@CR171]). These studies generally found minor effects of interventions for reducing or preventing child maltreatment. In specific, Geeraerts et al. ([@CR76]) found a small effect (*d* = .29) of early prevention interventions for families with young children at risk for physical child abuse and neglect. Filene et al. ([@CR69]) found a small effect (*d* = .20) of home visitation interventions, and Pinquart and Teubert ([@CR145]) found a very small but significant effect (*d* = .13) of parent education interventions for expectant and new parents. Euser et al. ([@CR61]) also found a very small but significant effect (*d* = 0.13) of interventions aimed at preventing or reducing child maltreatment. However, this last effect was no longer significant after publication bias was taken into account by applying the trim-and-fill approach.

A few meta-analyses have attempted to identify characteristics of child maltreatment interventions associated with intervention effectiveness by examining potential moderators of the mean effect of interventions. However, none of these meta-analyses extensively examined whether and how specific intervention components, such as different content or delivery methods, influence intervention effectiveness. In studies on child maltreatment interventions, different terms are used for intervention components, such as practice elements (Chorpita and Daleiden [@CR37]), kernels (Embry and Biglan [@CR60]), behavior change techniques (Michie et al. [@CR129]), and core components (Blase and Fixsen [@CR25]). Blase and Fixsen ([@CR25]) classify core components into: (1) contextual factors, such as types of families served (e.g., low-income teenage parents, parents with alcohol or drug problems) and delivery settings (e.g., clinic-based therapy, home visits), (2) structural elements, such as the required number and specific sequence of sessions, and (3) specific intervention practices, such as teaching problem-solving behavior, practicing communication skills, and reinforcing appropriate behavior. Specific intervention practices can be further classified based on intervention content (such as increasing knowledge of typical child development, increasing parenting self-efficacy, and improving discipline and/or behavior management strategies) and delivery techniques used to engage parents and teach relevant content (such as group discussions, homework assignments, role-playing, and modeling).

The main objective of this meta-analysis was to determine whether and how intervention components (i.e., intervention content and delivery techniques) influence the effectiveness of child maltreatment interventions. In doing so, important insight can be gained into what components contribute to intervention effectiveness and, consequently, how child maltreatment interventions can best be designed to reach optimal effectiveness. For this purpose, we conducted a three-level meta-analysis in which we tested intervention components as potential moderators of the (mean) effect of child maltreatment interventions. As we aimed for a comprehensive meta-analysis, we included (a) two types of interventions: *preventive* interventions targeting the general population or families at risk for child maltreatment and *curative* interventions targeting maltreating families that are aimed at reducing maltreatment, (b) randomized controlled trials (RCTs) as well as high quality quasi-experimental studies, and (c) recently conducted studies, as previous meta-analyses included studies that were published until 2013.

Determining which components appear to be essential (or nonessential) across a variety of interventions aimed at reducing or preventing child maltreatment has important implications for clinical practice. First, when choosing among interventions to implement, such information could be used to select interventions containing components associated with greater intervention effectiveness. Second, the effectiveness of existing interventions could be improved by integrating specific components associated with greater effectiveness into interventions. Third, it may be possible to eliminate components associated with less effective interventions, thereby minimizing the burden on practitioners and families.

In the present study, we aimed to examine the effect of contextual factors (i.e., general aim of the intervention, types of families served, delivery setting, type of intervention, specific intervention, age of the children), structural elements (i.e., type of worker, duration of intervention, number and interval of intervention sessions), content (parenting skills, personal skills parents, self-confidence of parents, attitudes/expectations toward parenting, knowledge of typical child development, social network of family, relationship between parents, relationship between parent and child, parental mental health problems, parental empowerment, social/emotional support, well-being child, child skills, practical support, motivation to change), and delivery methods (i.e., modeling, role-playing, monitoring, (psycho) education, homework assignments, cognitive skills training, and family group conferencing). We also examined the effect of study design characteristics such as sample characteristics (i.e., sample size, age of parents, percentage of cultural minorities), design of the study (randomized controlled trial versus quasi-experimental), and outcome characteristics (follow-up duration, type of outcome measure).

Method {#Sec1}
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Inclusion Criteria {#Sec2}
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Studies were selected if they met the following three criteria. First, studies had to report on the effect of at least one intervention for preventing or reducing child maltreatment. In specific, we included two types of interventions: *preventive* interventions targeting the general population or targeting families at risk for child maltreatment and *curative* interventions targeting maltreating families aimed at reducing maltreatment or recurrence of maltreatment. In this review, we followed the definition of child maltreatment as formulated by the Centers for Disease Control and Prevention: "any act or series of acts of commission or omission by a parent or other caregiver that results in harm, potential for harm, or threat of harm to a child." Given this broad definition, we included studies that reported on interventions for physical abuse, sexual abuse, and neglect. In addition, studies examining the effect of child maltreatment interventions on harsh parenting (such as corporal/physical punishment or parental aggression toward children) and out-of-home placement were also included. Second, experimental studies as well as quasi-experimental studies (in which a treatment condition is compared to a control condition) were included. Although randomized controlled trials can be regarded as the "golden standard" for studies examining the effectiveness of interventions (Farrington [@CR63]), we decided to also include quasi-experimental studies, since RCTs are rather scarce in the field of child protection due to practical and ethical concerns for true experimental designs. Third, studies had to report at least one effect size or sufficient information to calculate at least one effect size.

Selection of Studies {#Sec3}
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The electronic databases PsychINFO, ERIC, PubMed, Web of Science, ScienceDirect, and Google Scholar were searched for articles, books, chapters, dissertations, and reports. Until March 2017, studies were collected using keywords regarding study design, intervention features, study outcomes, and participants in different combinations: '(quasi-)experiment', 'randomized control\*', 'trial', 'RCT' 'child\*', 'abus\*', 'maltreat\*', 'neglect\*', 'interven\*', 'preven\*', 'home visit\*', 'recur\*', 'recidiv\*', 'relaps\*', 'family group conferencing' 'randomized', 'evaluat\*', and 'experiment\*'.

Next, manual searches of reference sections of the retrieved articles, reviews, and book chapters were conducted. Finally, we contacted authors by email to request for studies and unpublished manuscripts on the effect of child maltreatment interventions that may be relevant for inclusion in the present review. The search procedure is depicted in the flow diagram presented in Fig. [1](#Fig1){ref-type="fig"}. The search yielded 546 relevant studies of which 130 studies met the inclusion criteria.Fig. 1Flowchart of selection of studies for inclusion in meta-analysis

Study Coding {#Sec4}
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Following the guidelines of Lipsey and Wilson ([@CR116]), a coding scheme was developed to code all study design and intervention characteristics that could moderate the effect of child maltreatment interventions.

First, with regard to *study design characteristics*, we collected information on publication year, sample size, parental age, percentage of cultural minorities in samples, research design (RCT, quasi-experimental design), pilot/feasibility study (yes/no), follow-up length (in months), and type of outcome measure (self-report of parents, official reports, observations, hospital data, self-report of children). Second, we retrieved information on intervention characteristics, which we divided into contextual factors, structural elements, and specific intervention practices (content and delivery techniques). The *contextual factors* included the general aim of the intervention (reducing risk for child maltreatment versus reducing actual child maltreatment), type of families served (maltreating parents, general population, risk group identified by means of a questionnaire, risk group identified based on the presence of one or two risk factors), delivery setting (home/ambulant, treatment center, combination of locations), post-/prenatal intervention (postnatal, prenatal, postnatal and prenatal), type of intervention (cognitive behavioral therapy, home visitation interventions \[in which parents are visited at home and provided with information, support and/or training regarding child health, development and care\], parent training interventions \[aimed at learning specific parenting skills\], family-based/multisystemic interventions \[aimed at the whole family system/multiple social systems\], substance abuse intervention \[primarily targeting substance abuse of parents\], before-school interventions, general prevention interventions \[aimed at preventing the occurrence of child maltreatment in the general population\], crisis interventions \[aimed at solving acute problems\], and combined interventions), specific individual interventions (ACT Parenting Raising Safe Kids, (Early) Head Start, PCIT, FGC/FCDM, Healthy Families, Healthy Start, Healthy Steps, Intensive Family Preservation Services, Incredible Years, MST (CAN/BSF), Nurse Family Partnership (NFP), Triple P, Parents as Teachers, Project 12-Ways, Safe Environment for Every Kid, Child Parent Enrichment Program, SafeCare, other), and age of the child (unborn child/baby (\< 2), infant/toddler (2--5), primary school (6--12), high school (\> 12). The *structural elements* included type of worker (professionals only versus professionals and others), the duration of the intervention (0--6 months, 7--12 months, 13--24 months, \> 24 months), the minimum duration of the intervention, the maximum duration of the intervention, the average number of sessions, and the interval of the sessions (weekly, multiple sessions a week, every other week/monthly, ascending/descending intensity, every 3 months). The *specific intervention practices (content)* included parenting skills (yes/no), personal skills of parents (yes/no), parents' self-confidence (yes/no), attitudes or expectations about parenting (yes/no), knowledge of typical child development (yes/no), social network of the family (yes/no), relationship between parents (yes/no), relationship between parent and child (yes/no), mental health problems parents (yes/no), parental empowerment (yes/no), social or emotional support (yes/no), well-being of the child (yes/no), child skills (yes/no), practical support (yes/no), and motivation (yes/no). Finally, we examined the following delivery techniques: modeling (yes/no), role-playing (yes/no), monitoring (yes/no), (psycho)education (yes/no), homework assignments (yes/no), cognitive skills training (yes/no), and family group conferencing (yes/no). Inter-rater agreement was based on a double-coding of 14 studies by two independent coders. An inter-rater agreement of 97% was found between the two coders on all coded variables.

Calculation of Effect Sizes {#Sec5}
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All outcomes of the primary studies were transformed into the standardized difference between two means, also referred to as Cohen's *d.* The effect sizes were calculated using formulas of Ferguson ([@CR65]), Lipsey and Wilson ([@CR116]), and Rosenthal ([@CR152]). In most instances, proportions, means and standard deviations, and odd ratios were transformed into Cohen's *d*. If insufficient statistical information was provided for calculating an effect size, we contacted the study authors and asked for the required information. In calculating each effect size, it was important that the direction of the effect (positive or negative) corresponded with the statistical data reported in the primary study. A positive effect indicated less child maltreatment (or levels of other factors, such as harsh parenting) was found in the intervention group than in the control group, whereas a negative effect indicated more child maltreatment in the intervention group than in the control group. If results were reported to be nonsignificant and additional statistical information required for calculating an effect size was not reported, the value of zero was assigned to an effect and added to the data set (Durlak and Lipsey [@CR55]).

All coded data and calculated effect sizes were entered in SPSS version 22. Before the analyses were performed, continuous variables were centered around their mean, and categorical variables were recoded into dummy variables for each category of a variable. Further, extreme values of effect sizes and sample sizes (*Z* \> 3.29 or *Z* \< − 3.29; Tabachnik and Fidell [@CR174]) were identified.

Statistical Analyses {#Sec6}
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For estimating the overall effect for all included child maltreatment interventions, only preventive interventions, and only curative interventions, as well as for examining potential moderating variables, a three-level meta-analysis technique was used. By applying a multilevel approach to meta-analysis, there is no need for aggregating or selecting data, implying that all relevant effect sizes can be extracted from primary studies (see also Assink et al. [@CR14]; Assink and Wibbelink [@CR15]). As a result, all information from primary studies is preserved and maximum statistical power can be achieved. In our meta-analytic model, three forms of variance were taken into account: random sampling variation of observed effect sizes (level 1), variance within studies (level 2), and variance between studies (level 3) (Cheung [@CR36]; Hox [@CR91]; Van den Noortgate et al. [@CR178], [@CR179]). The sampling variance (level 1) was not estimated, but considered to be known and calculated using the formula of Cheung ([@CR36], p. 2015). Because we considered the primary studies to be a random sample from a larger population of studies, we built random-effects models.

Estimating the overall effects was done in separate three-level intercept-only models. Effect sizes were weighted by the inverse of their variance (i.e., sampling error), so that effect sizes derived from studies using samples of larger size contributed more to the overall effect size estimate than effect sizes derived from studies using samples of smaller size. Next, the significance of the variance distributed on levels 2 and 3 were tested by conducting two separate one-tailed log-likelihood ratio tests. In these tests, the deviance of a model in which the variance on either level 2 or level 3 was set to zero, was compared to the deviance of the full model in which level 2 and level 3 variances were freely estimated. In case the level 2 and/or level 3 variance was significant, the distribution of effect sizes was considered to be heterogeneous. This indicates that the effect sizes could not be treated as estimates of one common effect size, and thus, moderator analyses were performed to search for variables that can explain the variance. Potential moderating variables (i.e., study design characteristics, contextual factors, structural elements, and specific intervention practices) were examined by testing them in a three-level meta-analytic model as covariates. In all meta-analytic models, the Knapp and Hartung correction (Knapp and Hartung [@CR104]) was applied, implying that the significance of coefficients was tested using the *t*- and *F*- distributions rather than the *z*-distribution.

The statistical software package R (version 3.2.0) and the metafor package (Viechtbauer [@CR182]) were used to build the 3-level meta-analytic models. We used the syntax as described by Assink and Wibbelink ([@CR15]). In all analyses, a 5% significant level was used.

Publication Bias and Sensitivity Analyses {#Sec7}
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A common problem in conducting a meta-analysis is that studies with nonsignificant or negative results are less likely to be published than studies with positive and significant results. This phenomenon is called publication bias and is often referred to as the 'file drawer problem' (Rosenthal [@CR153]). So, the effects extracted from primary studies included in this meta-analysis may not be an adequate representation of the actual effect of child maltreatment interventions. Besides publication bias, the results may be affected by other forms of bias, such as coding or selection bias. Therefore, we examined the degree to which our results were affected by (different forms of) bias by conducting the nonparametric and funnel plot-based trim-and-fill analysis as described by Duval and Tweedie ([@CR56], [@CR57]). A funnel plot is a scatter plot of the effect sizes against the effect size's precision (1 divided by the standard error). In this analysis, the symmetry of the funnel is tested, as the plot would be asymmetric when bias is present. In case of an asymmetric plot, the asymmetry is restored by imputing "missing" effect sizes that are estimated on the basis of existing effect sizes in the data set. Subsequently, a "corrected" overall effect can be estimated in a sensitivity analysis using the data set to which the imputed effect sizes produced by the trim-and-fill algorithm have been added. In this way, the degree to which the results were affected by bias can be made visible.

As we identified seven outlying effect sizes (see above), we performed a sensitivity analysis in which we estimated an overall effect of child maltreatment interventions using the data in which the outlying effect sizes were excluded. In this way, we could determine the degree to which the initially estimated overall effect was robust against outliers in effect sizes. In addition, we estimated the overall effect of child maltreatment interventions excluding the results of pilot/feasibility studies, because these studies are more likely to show an effect that is larger than effects produced by well-powered trials.

Results {#Sec8}
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Descriptive Characteristics {#Sec9}
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The present meta-analysis included 130 studies with *k* = 121 non-overlapping samples, comprising *N* = 39.044 participants. A total of 352 effect sizes were extracted from all primary studies, which examined the effect of home visitation interventions (*k* = 50), parent training interventions (*k* = 29), family-based/multisystemic interventions (*k* = 17), substance abuse interventions (*k* = 4), before-school interventions (*k* = 4), general prevention interventions (*k* = 4), crisis interventions (*k* = 3), cognitive behavioral therapy (*k* = 2), and combined interventions (*k* = 15). These studies were published between 1977 and 2017 (with 2007 being the median publication year) and were conducted in the USA (*k* = 93), Europe (*k* = 11), Canada (*k* = 6), Australia or New Zealand (*k* = 6), and in various other countries (*k* = 5). The characteristics of the studies are presented in "[Appendix 1](#Sec18){ref-type="sec"}," including the name of the child maltreatment intervention, publication year, sample size, age of the child at the start of the intervention, study design (RCT or quasi-experimental), and type of families served (risk group, general population, or maltreating parents). The distribution of the moderators for preventive and curative interventions is presented in Table [1](#Tab1){ref-type="table"}.Table 1Distribution of moderators separately for preventive and curative interventionsPreventive interventions (*n* = 91) (%)Curative interventions *(n* = 32) (%)*χ* ^2^(*df*)Research design1.31(1) Randomized controlled trial68.156.7 Quasi-experimental31.943.4Type of outcome measure3.21(2) Self-report parents58.243.3 Official reports35.253.3 Other (observations, self-report child)6.63.3Type of worker14.90(2)\*\*\* Only professionals48.889.7 Professionals and others51.210.3Delivery setting1.03(2) Home/ambulant54.748.0 Treatment center22.132.0 Combination of locations23.320.0Age of the child42.5(2)\*\*\* 2 years or younger67.87.7 2--5 years old21.823.1 6 year or older10.369.2Duration13.5(3)\* 0--6 months38.858.3 7--12 months5.920.8 13--24 months25.920.8 \> 24 months29.40.0Type of intervention51.1(7)\*\*\* Home visitation intervention48.416.7 Parenting training25.320.0 Family-based/multisystemic4.446.7 Substance-abuse intervention0.010.0 Before-school intervention3.30.0 General prevention intervention4.40.0 Crisis intervention1.16.7 Combined interventions13.20.0Specific intervention practices Improving parental skills76.970.0.58(2) Improving personal skills parents38.570.09.03(2)\*\* Increasing parent's self-confidence19.820.0.01(2) Improving attitudes/expectations toward parenting11.03.31.60(2) Improving knowledge of typical child development63.713.322.94\*\*\* Strengthening social network27.543.32.64(2) Improving relationship between parents13.220.0.83(2) Improving relationship between parent-- child50.546.7.14(2) Addressing parental mental health problems23.136.72.14(2) Empowerment23.133.31.25(2) Social/emotional support49.523.36.28(2)\* Improving well-being child51.640.01.23(2) Improving child skills15.420.0.35(2) Practical support27.533.3.38(2) Improving motivation3.323.311.95(2)\*\*Delivery techniques Modeling34.622.21.43(2) Discussion44.940.7.14(2) Role-playing11.533.36.71(2)\*\* Monitoring23.118.5.24(2) Psycho(education)71.825.917.58(2)\*\*\* Homework assignments9.022.23.25(2)^+^ Cognitive skills training3.825.911.35(2)\*\* Family group conferencing2.622.211.01(2)\*\*\**df* Degrees of freedom\* *p* \< .05; \*\**p* \< .01; \*\*\* *p* \< .001^+^ *p* \< .1

Overall Effect, Heterogeneity in Effect Sizes, and Sensitivity Analyses {#Sec10}
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A significant overall effect was found of interventions aimed at preventing or reducing child maltreatment with a Cohen's *d* of 0.287; 95% CI \[0.226; 0.348\], *t*(351) = 9.209, *p* \< .001 (see Table [2](#Tab2){ref-type="table"}). According to the criteria formulated by Cohen ([@CR38]), this effect is small in magnitude. The two log-likelihood ratio tests showed that significant variance was present both at level 2 (*χ* ^2^(1) = 178.015, *p* \< .001; one-sided) and level 3 (*χ* ^2^(1) = 48.182, *p* \< .001; one-sided) of the meta-analytic model. Of the total variance, 32.8 and 56.1% were distributed at levels 2 and 3, respectively, and 11.1% was the percentage of sampling variance that was calculated using the formula of Cheung ([@CR36], p. 2015).Table 2Overall Effect for all interventions, preventive interventions, curative interventions, and all interventions excluding pilot/feasibility studies\# Studies\# ESMean *d* (SE)95% CISig. mean *d* (*p*)% Var. at level 1Level 2 variance% Var. at level 2Level 3 variance% Var. at level 3All interventions1213520.287 (0.031)\*\*\*0.226, 0.348\< .001\*\*\*11.110.043\*\*\*32.760.073\*\*\*56.13Preventive interventions912170.263 (0.034)\*\*\*0.197, 0.329\< .001\*\*\*9.440.028\*\*\*26.430.067\*\*\*64.13Curative interventions321350.364 (0.069)\*\*\*0.227, 0.502\< .001\*\*\*21.260.147\*\*\*55.700.061\*23.04All interventions excluding pilot/feasibility studies1143320.278 (0.032)\*\*\*0.215, 0.341\< .001\*\*\*10.56.045\*\*\*34.22.072\*\*\*55.22\# *Studies* number of studies; \# *ES* number of effect sizes, *Mean d* mean effect size (Cohen's *d*), *SE* standard error, *CI* confidence interval, *Sig* significance,  *% Var* percentage of distributed variance, *level 1* variance sampling variance, *level 2 variance* variance within studies, *level 3 variance* variance between studies\**p* \< .05; \*\*\**p* \< .001

The results of the trim-and-fill analysis showed that bias may be present in the data, as the distribution of all effect sizes (produced by both preventive and curative interventions) was asymmetrical. Figure [2](#Fig2){ref-type="fig"} shows that a small number of effect sizes had to be imputed in the right side of the funnel to restore its symmetry. In specific, 3 effect sizes from 2 independent studies were added to the data and after re-estimating the overall effect, a slightly higher (Δ*d* = 0.014) significant effect was found (*d* = 0.301 \[95% CI 0.238; 0.365\], *t*(354) = 9.343, *p* \< .001). Besides asymmetry in the distribution of effect sizes, there were a number of effect sizes that seemed to be "outliers" compared with other effect sizes (i.e., the effects in the most right part of Fig. [2](#Fig2){ref-type="fig"}). To determine whether and how these "outlying" effect sizes influenced our estimated overall effect, we performed a sensitivity analysis in which we re-estimated an overall effect after excluding 7 effect sizes with a *Z* score exceeding 3.29 (Tabachnik and Fidell [@CR174]) from the data. The results produced an overall effect of *d* = 0.257; 95% CI \[0.204, 0.311\], *t*(344) = 9.499, *p* \< .001, which is slightly below our initial estimated overall effect (Δ*d* = 0.030). In addition, we estimated the overall effect of all interventions using data without effects derived from the pilot studies (see Table [2](#Tab2){ref-type="table"}). The influence of pilot/feasibility studies on the overall summary effect was only small (*d* = 0.287 with pilot/feasibility studies and *d* = 0.278 without pilot/feasibility studies; Δ*d* = 0.009). All three sensitivity analyses showed that the estimated overall effect of *d* = 0.287 was rather robust.Fig. 2Funnelplot

Next, we estimated an overall effect of only preventive interventions, and this yielded a Cohen's *d* of 0.263; 95% CI \[0.197; 0.329\], which is a small effect according to the criteria of Cohen ([@CR38]). The two log-likelihood ratio tests showed once again that significant variance was present at level 2 (*χ* ^2^(1) = 141.121, *p* \< .001; one-sided) and level 3 (*χ* ^2^(1) = 45.038, *p* \< .001; one-sided) of the meta-analytic model. Of the total variance, 26.4 and 64.1% were distributed at levels 2 and 3, respectively, and 9.4% was distributed at level 1. As these results indicated substantial heterogeneity in effect sizes, we could test study design and intervention characteristics as potential moderators of the effect of preventive interventions. The estimated overall effect of curative interventions was also significant with a Cohen's *d* of 0.364; 95% CI \[0.227; 0.502\] and was small in magnitude according to Cohen's criteria. Both the level 2 variance (*χ* ^2^(1) = 55.467, *p* \< .001; one-sided) and the level 3 variance (*χ* ^2^(1) = 3.975, *p* = .023; one-sided) were significant, and of the total variance, 21.3, 55.7, and 23.0% were distributed at levels 1, 2, and 3, respectively. So, also for curative interventions, moderator analyses could be performed to examine whether and how the intervention effect was influenced by study design and intervention characteristics.

Moderator Analyses Bivariate Models {#Sec11}
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Table [3](#Tab3){ref-type="table"} shows the results of the moderator analyses performed for the preventive interventions, and Table [4](#Tab4){ref-type="table"} shows the results of the moderator analyses performed for the curative interventions.Table 3Results of the moderator analyses for preventive interventions (bivariate models)Moderator variables\# Studies\# ESIntercept/mean *d* (95% CI)*β* ~1~ (95% CI)*F* (*df*1, *df*2)^a^*p* ^b^Level 2 varianceLevel 3 varianceOverall effect912170.263 (0.197, 0.329)\*\*\***A: Study design characteristics**Publication year912170.264 (0.197, 0.330)\*\*\*0.002 (− 0.005, 0.009)0.211 (1, 215).646.028\*\*\*.068\*\*\**Sample characteristics*Sample size912170.263 (0.197, 0.330)\*\*\*− 0.000 (− 0.000, 0.000)2.559 (1, 215).111.027\*\*\*.069\*\*\*Age of the parents18490.377 (0.239, 0.515)\*\*\*0.013 (− 0.015, 0.040)0.865 (1, 47).357.000.060\*\*\*Percentage cultural minorities631630.817 (− 0.084, 1.718)^+^0.190 (− 0.084, 0.464)1.867 (1, 161).174.023\*\*\*.063\*\*\**Design characteristics*Research design3.720 (1, 215).055^+^.028\*\*\*.064\*\*\* RCT (RC)631590.226 (0.151, 0.301)\*\*\* Quasi-experimental29580.347 (0.238, 0.455)\*\*\*0.121 (− 0.003, 0.245)^+^Pilot/feasibility study0.009 (1, 215).922.028\*\*\*.068\*\*\* No (RC)872130.263 (0.195, 0.330)\*\*\* Yes440.282 (− 0.111, 0.676)0.020 (− 0.380, 0.419)*Outcome characteristics*Follow-up period40800.261 (0.150, 0.372)\*\*\*0.002 (0.000, 0.003)\*5.480 (1, 78).022\*.014\*\*\*.092\*\*\*Type of outcome measure1.727 (2, 214).180.027\*\*\*.068\*\*\* Self-report parents (RC)621470.296 (0.221, 0.371)\*\*\* Official reports41580.213 (0.120, 0.305)\*\*\*− 0.083 (− 0.179, 0.012)^+^ Other7120.200 (− 0.012, 0.413)^+^− 0.095 (− 0.311, 0.120)**B: Contextual factors**Type of families served0.686 (2, 214).505.028\*\*\*.069\*\*\*Risk group (questionnaire) (RC)361040.308 (0.205, 0.411)\*\*\*Risk group (risk factor)49950.226 (0.133, 0.319)\*\*\*− 0.082 (− 0.221, 0.057)General population8180.266 (0.061, 0.472)\*\*\*− 0.042 (− 0.271, 0.188)General aim of the intervention0.014 (1, 215).906.028\*\*\*.069\*\*\* Reducing risk (RC)851990.262 (0.194, 0.331)\*\*\* General prevention8180.275 (0.071, 0.479)\*\*0.013 (− 0.197, 0.223)Delivery setting0.772 (2, 208).463.026\*\*\*.072\*\*\* Home/ambulant (RC)471250.288 (0.195, 0.381)\*\*\* Treatment center19450.273 (0.128, 0.418)\*\*\*− 0.015 (− 0.188, 0.158) Combination of locations21410.185 (0.046, 0.323)\*\*− 0.103 (− 0.270, 0.064)Post/prenatal1.571 (2, 212).210.028\*\*\*.065\*\*\* Postnatal (RC)541350.304 (0.219, 0.389)\*\*\* Prenatal4110.293 (0.060, 0.527)\*− 0.010 (− 0.256, 0.235) Prenatal and postnatal34690.187 (0.080, 0.293)\*\*\*− 0.117 (− 0.253, 0.019)^+^Type of intervention3.616 (7, 209).001\*\*\*.028\*\*\*.050\*\*\* Home visitation intervention (RC)451050.210 (0.126, 0.293)\*\*\* Parent training23560.428 (0.305, 0.551)\*\*\*0.218 (0.070, 0.367)\*\* Family-based/multisystemic470.343 (0.027, 0.660)\*0.134 (− 0.194, 0.461) Substance-abuse intervention111.852 (0.933, 2.770)\*\*\*1.642 (0.720, 2.564)\*\*\* Before-school intervention480.148 (− 0.117, 0.413)− 0.062 (− 0.335, 0.212) General prevention4160.024 (− 0.219, 0.267)− 0.186 (− 0.442, 0.071) Crisis intervention120.407 (− 0.114, 0.929)0.198 (− 0.330, 0.726) Combined intervention15220.174 (0.024, 0.324)\*− 0.036 (− 0.203, 0.131)Specific individual interventions0.552 (13, 203).889.027\*\*\*.080\*\*\* Other interventions (RC)49840.311 (0.211, 0.411)\*\*\* ACT parents raising safe kids360.377 (− 0.013, 0.768)^+^0.066 (− 0.337, 0.469) (Early) head start5120.074 (− 0.208, 0.357)− 0.237 (− 0.537, 0.063) Healthy families10350.189 (− 0.004, 0.382)^+^− 0.123 (− 0.340, 0.095) Healthy start4120.339 (0.012, 0.666)\*0.028 (− 0.314, 0.369) Healthy steps2100.189 (− 0.235, 0.614)− 0.122 (− 0.558, 0.314) Intensive fam preservation serv120.407 (− 0.217, 1.030)0.095 (− 0.536, 0.727) Incredible years3110.307 (− 0.085, 0.699)− 0.005 (− 0.409, 0.400) NFP270.298 (− 0.146, 0.741)− 0.013 (− 0.468, 0.441) Triple P4180.417 (0.092, 0.741)\*0.105 (− 0.234, 0.445) Parents as teachers240.079 (− 0.376, 0.535)− 0.232 (− 0.698, 0.234) Safe environment for every Kid270.058 (− 0.360, 0.475)− 0.254 (− 0.683, 0.176) Child--parent enrichment progr.240.102 (− 0.375, 0.580)− 0.209 (− 0.697, 0.279) SafeCare130.139 (− 0.491, 0.768)− 0.173 (− 0.811, 0.465)Age of the child1.162 (3, 200).325.028\*\*\*.069\*\*\* Unborn child/baby (≤ 2) (RC)591320.222 (0.140, 0.304)\*\*\* Infant/toddler (2--5)19530.365 (0.219, 0.512)\*\*\*0.143 (− 0.025, 0.311)^+^ Primary school (6--12)9170.305 (0.104, 0.505)\*\*0.083 (− 0.127, 0.292) High school (≥ 12)120.465 (− 0.188, 1.118)0.243 (− 0.415, 0.902)**C: Structural elements**Type of worker4.789 (1, 207).030\*.028\*\*\*.065\*\*\* Only professionals (RC)411090.334 (0.236, 0.432)\*\*\* Professionals and others461000.184 (0.091, 0.277)\*\*\*− 0.150 (− 0.285, − 0.015)\*Duration4.484 (3, 199).005\*\*.021\*\*\*.047\*\*\* 0--6 months (RC)25820.361 (0.268, 0.454)\*\*\* 7--12 months58− 0.051 (− 0.295, 0.192)− 0.412 (− 0.673, − 0.152)\*\* 13--24 months23410.236 (0.119, 0.354)\*\*\*− 0.124 (− 0.273, 0.024)^+^  \> 24 months25720.190 (0.090, 0.289)\*\*\*− 0.171 (− 0.302, − 0.041)\*Minimum duration (in weeks)23490.343 (0.198, 0.488)\*\*\*− 0.002 (− 0.004, 0.001)2.303 (1, 47).136.026\*\*\*.067\*Maximum duration (in weeks)621520.242 (0.173, 0.311)\*\*\*− 0.001 (− 0.002, − 0.000)\*6.337 (1, 150).013\*.020\*\*\*.043\*\*\*Average number of sessions43960.243 (0.145, 0.340)\*\*\*− 0.001 (− 0.008, 0.006)0.133 (1, 94).716.005.077\*\*\*Interval sessions1.345 (4, 153).256.018\*\*\*.056\*\*\* Weekly (RC)30630.352 (0.244, 0.461)\*\*\* Multiple sessions a week480.325 (0.025, 0.626)\*− 0.027 (− 0.346, 0.292) Every other week/monthly12200.277 (0.119, 0.435)\*\*\*− 0.075 (− 0.267, 0.116) Ascending/descending intensity25620.185 (0.075, 0.295)\*\*− 0.167 (− 0.319, − 0.015)\* Every 3 months150.107 (− 0.380, 0.595)− 0.245 (− 0.745, 0.254)**C: Specific intervention practices (content)**Parenting skills1.513 (1, 215).220.028\*\*\*.067\*\*\* No (RC)21480.188 (0.051, 0.325)\*\* Yes711690.284 (0.210, 0.359)\*\*\*0.096 (− 0.058 0.251)Personal skills parents0.083 (1, 215).774.028\*\*\*.068\*\*\* No (RC)561130.255 (0.167, 0.343)\*\*\* Yes361040.274 (0.173, 0.376)\*\*\*0.020 (− 0.114, 0.154)Parents' self-confidence4.389 (1, 215).037\*.027\*\*\*.067\*\*\* No (RC)731800.229 (0.156, 0.302)\*\*\* Yes21370.397 (0.255, 0.539)\*\*\*0.168 (0.010, 0.325)\*Attitudes/expectations toward parenting1.486 (1, 215).224.028\*\*\*.066\*\*\* No (RC)812020.250 (0.181, 0.319)\*\*\* Yes10150.391 (0.173, 0.608)\*\*\*0.141 (− 0.087, 0.369)\*\*\*Knowledge of typical child development0.710 (1, 215).400.028\*\*\*.067\*\*\* No (RC)33760.300 (0.190, 0.411)\*\*\* Yes591410.243 (0.161, 0.324)\*\*\*− 0.058 (− 0.193, 0.078)Social network of family0.068 (1, 215).795.028\*\*\*.069\*\*\* No (RC)661530.269 (0.190, 0.348)\*\*\* Yes26640.249 (0.124, 0.375)\*\*\*− 0.020 (− 0.167, 0.128)Relationship between parents0.443 (1, 215).506.029\*\*\*.066\*\*\* No (RC)801850.270 (0.201, 0.339)\*\*\* Yes14320.217 (0.069, 0.366)\*\*− 0.053 (− 0.208, 0.103)\*\*\*Relationship between parent and child0.379 (1, 215).539.028\*\*\*.069\*\*\* No (RC)451070.243 (0.148, 0.337)\*\*\* Yes471100.284 (0.190, 0.379)\*\*\*0.042 (− 0.092, 0.175)Mental health problems parents0.148 (1, 215).701.028\*\*\*.069\*\*\* No (RC)711590.256 (0.180, 0.333)\*\*\* Yes22580.286 (0.154, 0.417)\*\*\*0.029 (− 0.121, 0.179)Empowerment0.555 (1, 215).457.028\*\*\*.068\*\*\* No (RC)701490.278 (0.201, 0.355)\*\*\* Yes22680.221 (0.092, 0.350)\*\*\*− 0.057 (− 0.207, 0.093)Social/emotional support0.450 (1, 215).503.028\*\*\*.067\*\*\* No (RC)461010.286 (0.191, 0.382)\*\*\* Yes461160.242 (0.152, 0.332)\*\*\*− 0.044 (− 0.174, 0.086)Well-being child2.142 (1, 215).145.028\*\*\*.065\*\*\* No (RC)45940.314 (0.218, 0.409)\*\*\* Yes481230.220 (0.133, 0.306)\*\*\*− 0.094 (− 0.221, 0.033)Child skills0.018 (1, 215).893.028\*\*\*.069\*\*\* No (RC)771820.262 (0.189, 0.334)\*\*\* Yes15350.273 (0.113, 0.434)\*\*\*0.012 (− 0.162, 0.186)Practical support1.046 (1, 215).308.028\*\*\*.067\*\*\* No (RC)671570.283 (0.206, 0.359)\*\*\* Yes26600.207 (0.082, 0.333)\*\*− 0.075 (− 0.220, 0.070)\*\*\*Motivation1.517 (1, 215).219.028\*\*\*.067\*\*\* No (RC)882090.271 (0.204, 0.339)\*\*\* Yes380.055 (− 0.283, 0.394)− 0.216 (− 0.561, 0.130)**D: Delivery techniques**Modeling0.842 (1, 184).360.024\*\*\*.078\*\*\* No (RC)521120.253 (0.161, 0.346)\*\*\* Yes27740.327 (0.199, 0.455)\*\*\*0.073 (− 0.084, 0.231)Role-playing1.025 (1, 184).313.025\*\*\*.075\*\*\* No (RC)701640.264 (0.186, 0.343)\*\*\* Yes9220.384 (0.164, 0.603)\*\*\*0.120 (− 0.113, 0.352)Monitoring1.898 (1, 184).170.025\*\*\*.076\*\*\* No (RC)611450.307 (0.222, 0.392)\*\*\* Yes18410.184 (0.031, 0.338)\*− 0.122 (− 0.297, 0.053)(Psycho) education1.712 (1, 184).192.025\*\*\*.072\*\*\* No (RC)22500.355 (0.216, 0.493)\*\*\* Yes581360.249 (0.164, 0.333)\*\*\*− 0.106 (− 0.266, 0.054)Homework assignments0.709 (1, 184).401.024\*\*\*.076\*\*\* No (RC)721600.268 (0.189, 0.346)\*\*\* Yes7260.374 (0.137, 0.612)\*\*0.107 (− 0.143, 0.357)Cognitive skills training1.784 (1, 184).183.024\*\*\*.078\*\*\* No (RC)761770.268 (0.192, 0.344)\*\*\* Yes490.504 (0.163, 0.846)\*\*0.236 (− 0.113, 0.585)Family group conferencing0.246 (1, 184).620.024\*\*\*.077\*\*\* No (RC)771840.276 (0.201, 0.351)\*\*\* Yes220.424 (− 0.161, 1.010)0.148 (− 0.442, 0.739)\# *Studies* number of studies, \# *ES* number of effect sizes, *mean d* mean effect size (Cohen's *d*), *CI* confidence interval, *β* ~1~ estimated regression coefficient, *df* degrees of freedom, *level 2 variance* variance within studies, *Level 3 variance* variance between studies\**p* \< .05; \*\**p* \< .01; \*\*\**p* \< .001^+^ *p* \< .1^a^Omnibus test of al regression coefficients of the model^b^ *p* value of the omnibus test Table 4Results of the moderator analyses for curative interventions (bivariate models)Moderator variables\# Studies\# ESIntercept/mean *d* (95% CI)*β* ~1~ (95% CI)*F* (*df*1, *df*2)^a^*p* ^b^Level 2 varianceLevel 3 varianceOverall effect321350.364 (0.227, 0.502)\*\*\***A: Study design characteristics**Publication year321350.396 (0.252, 0.540)\*\*\*− 0.013 (− 0.031, 0.006)1.889 (1, 133).172.144\*\*\*.060\**Sample characteristics*Sample size321350.408 (0.267, 0.550)\*\*\*− 0.001 (− 0.002, 0.000)^+^3.489 (1, 133).064^+^.145\*\*\*.054\*Age of the parents12400.468 (0.218, 0.718)\*\*\*0.009 (− 0.046, 0.065)0.111 (1, 38).741.059\*\*\*.121\*\*\*Percentage cultural minorities201110.396 (0.270, 0.523)\*\*\*− 0.592 (− 1.239, 0.055)^+^3.284 (1, 109).073^+^.182\*\*\*.010*Design characteristics*Research design0.265 (1, 133).608.148\*\*\*.063\* RCT (RC)191150.340 (0.171, 0.509)\*\*\* Quasi-experimental13200.417 (0.173, 0.662)\*\*\*0.077 (− 0.220, 0.374)Pilot/feasibility study1.523 (1, 133).219.147\*\*\*.058^+^ No (RC)291190.333 (0.188, 0.478)\*\*\* Yes3160.594 (0.201, 0.986)\*\*0.261 (− 0.157, 0.679)*Outcome characteristics*Follow-up period22850.339 (0.168, 0.509)\*\*\*0.005 (− 0.008, 0.017)0.510 (1, 83).477.095\*\*\*.074^+^Type of outcome measure3.241 (2, 132).042\*.134\*\*\*.059\* Self-report parents (RC)14720.216 (0.033, 0.398)\*\*\* Official reports26390.498 (0.328, 0.668)\*\*\*0.282 (0.057, 0.508)\* Other4240.200 (− 0.075, 0.474)− 0.016 (− 0.265, 0.233)**B: Contextual factors**Delivery setting0.202 (2, 124).817.151\*\*\*.060\*Combination of locations (RC)5630.350 (0.028, 0.672)\*\*\*Home/ambulant13360.431 (0.217, 0.644)\*\*\*0.081 (− 0.305, 0.467)Treatment center9280.479 (0.220, 0.737)\*\*\*0.129 (− 0.273, 0.531)Post-/prenatal Postnatal (RC)291320.359 (0.215, 0.502)\*\*\*0.117 (1, 133).733.149\*\*\*.063\* Prenatal and postnatal330.459 (− 0.102, 1.020)0.100 (− 0.479, 0.679)Type of intervention0.119 (5, 129).988.150\*\*\*.084\* Family-based/multisystemic (RC)14600.346 (0.132, 0.561)\*\* Home visitation intervention6140.344 (− 0.009, 0.697)^+^− 0.003 (− 0.416, 0.411) Parent training6110.415 (0.025, 0.806)\*0.069 (− 0.376, 0.515) Substance abuse intervention3180.385 (− 0.025, 0.795)^+^0.039 (− 0.424, 0.501) Crisis intervention220.335 (− 0.376, 1.047)− 0.011 (− 0.754, 0.732) Cognitive behavioral therapy2300.445 (0.123, 0.767)\*\*0.098 (− 0.178, 0.375)Specific individual interventions0.375 (6, 128).894.148\*\*\*.081\* Other interventions (RC)171000.402 (0.200, 0.603)\*\*\* Parent--child interaction therapy390.270 (− 0.184, 0.724)− 0.132 (− 0.629, 0.365) FGC/FGDM580.133 (− 0.269, 0.535)− 0.268 (− 0.718, 0.181) Intensive fam preservation serv220.335 (− 0.369, 1.040)− 0.066 (− 0.799, 0.667) Incredible years240.461 (− 0.167, 1.089)0.060 (− 0.600, 0.719) MST (CAN/BSF)2100.545 (0.023, 1.068)\*0.143 (− 0.417, 0.703) Project 12-ways220.470 (− 0.235, 1.176)0.069 (− 0.665, 0.802)Age of the child0.163 (3, 122).921.160\*\*\*.074\* Primary school (6--12) (RC)17980.375 (0.176, 0.573)\*\*\* Unborn child/baby (≤ 2)330.460 (− 0.127, 1.047)0.086 (− 0.534, 0.706) Infant/toddler (2--5)7170.267 (− 0.045, 0.579)^+^− 0.108 (− 0.478, 0.262) High school (≥ 12)180.391 (− 0.236, 1.018)0.016 (− 0.641, 0.674)**C: Structural elements**Type of worker0.543 (1, 130).463.153\*\*\*.065 Professionals (RC)261250.353 (0.201, 0.506)\*\*\* Not only professionals470.524 (0.093, 0.955)\*0.170 (− 0.287, 0.627)Duration0.709 (3, 122).548.157\*\*\*.063\* 0--6 months (RC)15910.453 (0.251, 0.656)\*\*\* 7--12 months5150.311 (− 0.047, 0.668)^+^− 0.143 (− 0.546, 0.261) 13--24 months5190.190 (− 0.120, 0.500)− 0.263 (− 0.633, 0.107) 24 months110.437 (− 0.571, 1.446)− 0.016 (− 1.044, 1.013)Minimum duration9300.433 (0.185, 0.680)\*\*− 0.005 (− 0.022, 0.012)0.371 (1, 28).547.023.084^+^Maximum duration231210.407 (0.266, 0.548)\*\*\*− 0.002 (− 0.005, 0.001)1.601 (1, 119).208.163\*\*\*.031Average number of sessions13390.356 (0.198, 0.513)\*\*\*− 0.009 (− 0.027, 0.008)1.146 (1, 37).291.070\*\*\*.026Interval sessions0.387 (4, 111).818.172\*\*\*.062^+^ Weekly (RC)7800.430 (0.166, 0.695)\*\*\* Multiple sessions a week5140.452 (0.086, 0.817)\*0.021 (− 0.430, 0.472) Every other week/monthly120.885 (− 0.064, 1.835)^+^0.455 (− 0.530, 1.440) Ascending/descending intensity5190.344 (0.027, 0.662)\*− 0.086 (− 0.499, 0.327) Every 3 months110.108 (− 0.943, 1.159)− 0.323 (− 1.407, 0.761)**C: Specific intervention practices (content)**Parenting skills5.089 (1, 133).026\*.150\*\*\*.040 No (RC)10450.190 (− 0.006, 0.387)^+^ Yes23900.430 (0.290, 0.569)\*\*\*0.239 (0.029, 0.449)\* Personal skills parents3.063 (1, 133).082^+^.142\*\*\*.057\* No (RC)10200.177 (− 0.073, 0.559)^+^ Yes221150.440 (0.280, 0.600)\*\*\*0.263 (− 0.034, 0.559)^+^Parents' self-confidence1.252 (1, 133).265.144\*\*\*.062\* No (RC)261200.327 (0.174, 0.480)\*\*\* Yes6150.525 (0.209, 0.842)\*\*0.199 (− 0.153, 0.550)Attitudes/expectations parenting1.643 (1, 133).202.146\*\*\*.061\* No (RC)311050.354 (0.215, 0.492)\*\*\* Yes2300.529 (0.240, 0.818)\*\*\*0.176 (− 0.095, 0.446)Knowledge of typical child development1.059 (1, 133).305.152\*\*\*.054 No (RC)271240.393 (0.247, 0.538)\*\*\* Yes5110.194 (− 0.159, 0.547)− 0.199 (− 0.581, 0.183)Social network of family0.063 (1, 133).803.147\*\*\*.065\* No (RC)17950.348 (0.154, 0.541)\*\*\* Yes15400.383 (0.182, 0.585)\*\*\*0.035 (− 0.244, 0.315)Relationship between parents0.491 (1, 133).485.144\*\*\*.070\* No (RC)28920.379 (0.232, 0.526)\*\*\* Yes6430.297 (0.058, 0.536)\*− 0.082 (− 0.315, 0.150)Relationship between parent and child1.524 (1, 133).219.151\*\*\*.055 No (RC)18710.424 (0.259, 0.589)\*\*\* Yes15640.296 (0.124, 0.469)\*\*\*− 0.127 (− 0.332, 0.077)Mental health problems parents3.613 (1, 133).059^+^.142\*\*\*.056\* No (RC)20950.258 (0.086, 0.431)\*\* Yes12400.521 (0.309, 0.733)\*\*\*0.263 (− 0.011, 0.536)^+^Empowerment2.854 (1, 133).093^+^.151\*\*\*.047^+^ No (RC)201110.440 (0.282, 0.599)\*\*\* Yes12240.203 (− 0.025, 0.431)^+^− 0.237 (− 0.515, 0.041)^+^Social/emotional support4.581 (1, 133).034\*.149\*\*\*.042 No (RC)241210.296 (0.155, 0.437)\*\*\* Yes8140.649 (0.355, 0.942)\*\*\*0.352 (0.027, 0.678)\*Well-being child3.600 (1, 133).060^+^.144\*\*\*.053^+^ No (RC)14230.272 (0.108, 0.435)\*\* Yes181120.539 (0.313, 0.766)\*\*\*0.268 (− 0.011, 0.547)^+^Skills child2.282 (1, 133).133.146\*\*\*.058\* No (RC)26940.327 (0.183, 0.471)\*\*\* Yes7410.499 (0.276, 0.723)\*\*\*0.172 (− 0.053, 0.398)Practical support0.311 (1, 133).578.146\*\*\*.066\* No (RC)201080.335 (0.160, 0.510)\*\*\* Yes12270.417 (0.185, 0.649)\*\*\*0.082 (− 0.209, 0.373)Motivation2.2021 (1, 133).157.148\*\*\*.056^+^ No (RC)26920.400 (0.256, 0.544)\*\*\* Yes7430.239 (0.019, 0.459)\*− 0.161 (− 0.385, 0.063)**D: Delivery techniques**Modeling0.199 (1, 127).656.160\*\*\*.069\* No (RC)221160.378 (0.209, 0.548)\*\*\* Yes7130.294 (− 0.038, 0.627)^+^− 0.084 (− 0.457, 0.289)Role-playing0.091 (1, 127).764.158\*\*\*.072\* No (RC)201090.347 (0.169, 0.525)\*\*\* Yes9200.399 (0.108, 0.691)\*\*0.052 (− 0.290, 0.394)Monitoring1.073 (1, 127).302.161\*\*\*.060^+^ No (RC)231160.323 (0.160, 0.485)\*\*\* Yes6130.517 (0.183, 0.851)\*\*0.194 (− 0.177, 0.565)(Psycho) education1.144 (1, 127).287.162\*\*\*.061 No (RC)22850.391 (0.234, 0.549)\*\*\* Yes8440.266 (0.039, 0.494)\*− 0.125 (− 0.357, 0.106)Homework assignments1.951 (1, 127).165.161\*\*\*.060^+^ No (RC)23790.318 (0.160, 0.475)\*\*\* Yes7500.479 (0.256, 0.702)\*\*\*0.162 (− 0.067, 0.390)Cognitive skills training1.197 (1, 127).276.165\*\*\*.056 No (RC)23770.326 (0.169, 0.483)\*\*\* Yes8520.449 (0.232, 0.667)\*\*\*0.124 (− 0.100, 0.348)Family group conferencing1.529 (1, 127).218.154\*\*\*.070\* No (RC)221120.412 (0.241, 0.583)\*\*\* Yes7170.189 (− 0.124, 0.502)− 0.223 (− 0.580, 0.134)\# *Studies* number of studies, \# *ES* number of effect sizes, mean *d* mean effect size (Cohen's *d*), *CI* confidence interval, *β* ~1~ estimated regression coefficient, *df* degrees of freedom, *level 2 variance* variance within studies, *level 3 variance* variance between studies\**p* \< .05; \*\**p* \< .01; \*\*\**p* \< .001^+^ *p* \< .1^a^Omnibus test of al regression coefficients of the model^b^ *p* value of the omnibus test

*Study design characteristics* For preventive interventions, a trend significant moderating effect was found for research design (larger effect sizes were found in quasi-experimental designs (*d* = .374) versus RCTs (*d* = .226)), and a significant positive moderating effect was found for follow-up period (intervention effects increased as follow-up length increased). For curative interventions, a trend significant negative moderating effect was found for sample size (larger sample sizes yielded smaller effect sizes), and a trend significant negative moderating effect was found for percentage of cultural minorities in samples (higher percentages of minorities yielded smaller effect sizes). A significant effect was found for type of outcome measure (larger effect sizes were found for official reports compared to self-reports of parents).

*Contextual factors* For preventive interventions, a significant moderating effect was found for the type of intervention: The effect of parent training interventions (*d* = .428) and substance abuse interventions (*d* = 1.852) were significantly higher than home visitation interventions (*d* = .210). The types of preventive interventions that were effective in preventing child maltreatment were: home visitation interventions (*d* = .210), parent training interventions (*d* = .428), family-based/multisystemic interventions (*d* = .343), substance abuse interventions (*d* = 1.852) and combined interventions (*d* = .174). Before-school interventions (*d* = .148), general prevention interventions (*d* = .024), and crisis interventions (*d* = .407) did not have a significant effect on preventing child maltreatment (the latter probably due to lack of power). Types of curative interventions that were effective in reducing child maltreatment were home visitation interventions (*d* = .344; trend significant), parent training interventions (*d* = .415), family-based/multisystemic interventions (*d* = 0.346), substance abuse interventions (*d* = .385; trend significant), and cognitive behavioral therapy (*d* = .445). Crisis interventions (*d* = .335) did not have a significant effect on reducing child maltreatment, probably due to lack of power.

Further, the moderator analysis showed that the effect of any of the specific individual interventions did not significantly deviate from the effect of the reference category (i.e., other interventions). Specific individual interventions were tested as a separate category only if the effect of the intervention has been examined in at least two studies. Specific individual interventions with a (trend) significant effect on preventing or reducing child maltreatment were: MST-CAN/BSF (*d* = .545), Triple P (*d* = .417), ACT-Parent's Raising Safe Kids Program (*d* = .377), and Healthy Start (*d* = .339).

*Structural elements* For preventive interventions, higher effect sizes were found for interventions delivered by professionals only (*d* = .334) compared to interventions delivered by professionals and others (such as paraprofessionals or non-professionals; *d* = .184). Higher effect sizes were found for interventions with a shorter duration (*d* = .361 for 0--6 months) compared to interventions with a longer duration (*d* = −.051 for 7--12 months; *d* = .236 for 13--24 months (trend significant difference); and *d* = .190 for longer than 24 months). For curative interventions, none of the structural elements were significantly related to effect size.

*Specific interventions practices and delivery techniques* For preventive interventions, larger effect sizes were found for interventions focusing on increasing the self-confidence of parents (*d* = .397 versus *d* = .229). For curative interventions, larger effect sizes were found for improving parenting skills (*d* = .430 versus *d* = .190), improving personal skills of parents (*d* = .440 versus *d* = .177; trend significant difference), addressing mental health problems parents (*d* = .521 versus *d* = .258; trend significant difference), providing social and/or emotional support (*d* = .649 versus *d* = .296), and improving child well-being (*d* = .539 versus *d* = .272; trend significant difference). Smaller effect sizes were found for interventions focusing on empowerment (*d* = .203 versus *d* = .440; trend significant difference).

Moderator Analyses Multiple Moderator Models {#Sec12}
--------------------------------------------

Finally, the moderators that were significant in the bivariate models were tested jointly in a multiple moderator model for preventive and curative interventions separately. In this way, the unique contribution of moderators to the prediction of effect size could be examined (see Tables [5](#Tab5){ref-type="table"} and [6](#Tab6){ref-type="table"}). In the multiple moderator model for preventive interventions, heterogeneity in intervention effects was particularly explained by follow-up duration, parent training interventions (versus other interventions; trend significant), substance abuse interventions (versus other interventions), and a focus on increasing self-confidence of parents (versus interventions without this focus). In the multiple moderator model for curative interventions, heterogeneity in intervention effects was particularly explained by outcome measure, a focus on improving parenting skills (versus interventions without this focus), and providing social/emotional support (versus interventions without this practice; trend significant). In both models, multicollinearity did not seem to be a problem, since all variance inflation factors were below 1.302 and all tolerance statistics were above 0.768.Table 5Results of the multiple moderator model for preventive interventionsModerator variables*β* (SE)95% CI*t*-statisticIntercept0.111 (0.094)− 0.077, 0.2991.182Control variablesFollow-up duration0.002 (0.001)\*0.000, 0.0032.595Parent training (vs. other intervention types)0.180 (0.100)^+^− 0.019, 0.3791.805Substance abuse intervention (vs. other intervention types)1.404 (0.464)\*\*0.478, 2.3293.025Professional workers (vs. not only professionals)0.119 (0.090)− 0.062, 0.2991.313Intervention duration \> 6 months (vs. 0--6 months)− 0.119 (0.086)− 0.290, 0.052− 1.392Parents' self-confidence (vs. interventions without self-confidence in intervention content)0.275 (0.123)\*0.029, 0.5212.231*F* (*df*1, *df*2)6.117 (6, 69)\*\*\*Level 2 variance0.014\*\*\*Level 3 variance0.037\*\*\**Β* estimated regression coefficient, *SE* standard error, *CI* confidence interval, *F F*-statistic (omnibus test), *Level 2 variance* variance within studies, *Level 3 variance* variance between studies\**p* \< .05; \*\**p* \< .01; \*\*\**p* \< .001^+^ *p* \< .100 Table 6Results of the multiple moderator model for curative interventionsModerator variables*β* (SE)95% CI*t*-statisticIntercept− 0.029 (0.111)− 0.248, 0.190− 0.264Control variablesOfficial records (vs. other outcome types)0.273 (0.107)\*0.061, 0.4852.547Parenting skills (vs. interventions without parenting skills in intervention content)0.288 (0.100)\*\*0.089, 0.4862.867Social/emotional support (vs. interventions without support in intervention content)0.264 (0.155)^+^− 0.043, 0.5711.700*F* (*df*1, *df*2)6.180 (3, 131)\*\*\*Level 2 Variance0.130\*\*\*Level 3 Variance0.028*Β* estimated regression coefficient, *SE* standard error, *CI* confidence interval, *F F*-statistic (omnibus test), *Level 2 variance* variance within studies, *Level 3 variance* variance between studies\**p* \< .05; \*\**p* \< .01; \*\*\**p* \< .001^+^ *p* \< .100

Discussion {#Sec13}
==========

The aim of the present meta-analysis was to gain insight into components contributing to the effectiveness of child maltreatment interventions. Overall, a small but significant effect was found of interventions aimed at preventing or reducing child maltreatment (*d* = .287), which is in line with findings of previously conducted meta-analyses on the effect of these interventions (e.g., Geeraerts et al. [@CR76]; Filene et al. [@CR69]; MacLeod and Nelson [@CR121]). The results of the trim-and-fill analysis suggested that bias was present in the data, and therefore, a "corrected" overall effect was estimated, resulting in an effect size of *d* = 0.301. Because there are several methodological shortcomings regarding the trim-and-fill method (see the Limitations section), this corrected effect size should not be interpreted as a true effect size, but only as an indicator of (possible) bias in the data.

Larger effect sizes were found for curative interventions targeting maltreating parents (*d* = .364) than for preventive interventions targeting at-risk families/the general population (*d* = .263), but this difference did not reach significance. Euser et al. ([@CR61]) did find a significantly higher effect for interventions aimed at reducing child maltreatment in maltreating families than for interventions aimed at preventing child maltreatment in at-risk families/the general population. The finding that curative interventions are more effective than preventive interventions may be explained by a lower prevalence of child maltreatment in at-risk families/the general population than in maltreating families, making it "more difficult" to find significant differences between intervention and control groups (because of lower statistical power) and consequently, to prove the effectiveness of an intervention. Furthermore, the detection of child maltreatment in the general population/at-risk families is particularly difficult when official records are used, as many maltreatment occurrences are not officially reported to child protection services. So, in primary studies examining the effect of a preventive intervention and in which official records are used produce rather small effect sizes. Therefore, relatively large research groups and long follow-up periods are needed to increase the power. This may also be a possible explanation for the significant effect of the variable follow-up period (higher effect sizes were produced in longer follow-up periods): the longer the follow-up period, the higher the prevalence of child abuse in the research groups, the more likely a possible effect is detected.

Study Design Characteristics {#Sec14}
----------------------------

For preventive interventions, higher effect sizes were found for studies with quasi-experimental designs (*d* = .347) than for RCTs (*d* = .226; trend significant difference). Previous meta-analyses that included only RCT designs generally showed smaller effect sizes than meta-analysis including both RCTs and quasi-experimental designs, which is in line with the findings of our meta-analysis. For example, Pinquart and Teubert ([@CR145]) found a very small effect (*d* = .13) of RCTs on parenting interventions for families with newborns. Euser et al. ([@CR61]) also found a very small effect (*d* = 0.13) of RCTs on interventions for preventing or reducing child maltreatment. Ultimately, exclusively reviewing RCT studies is desirable, because effects of child maltreatment interventions can best be determined in RCT's, as random assignment of participants to an experimental and a control group (theoretically) equalizes both groups on all other variables. Therefore, RCT's are considered to be the most powerful study design in intervention research. However, at present, it is too early for such a review, because only a few RCTs have been performed on the effectiveness of child maltreatment interventions and their components. Consequently, a lot of essential information would be missing in a review of only RCTs and as a result, little knowledge could be obtained about effective components. Additionally, when matching procedures are properly applied in quasi-experimental studies, reasonable control groups can be formed so that generalization of results is quite feasible and realistic.

Further, for preventive interventions, larger positive intervention effects were found at later follow-up than at immediate post-intervention, which may be attributed to sleeper effects of interventions (Maurer et al. [@CR126]). Sleeper effects in the context of child maltreatment interventions imply that positive intervention effects---at least to some extent---need time to emerge after interventions have ended. For example, parents may be unsure about applying newly learned parenting practices in their own home environment without being helped or supervised and, consequently, time passes until parents are able to apply these practices effectively. As soon as parents have practiced and acquired more confidence, the newly learned practices may be reinforced by positive responses of the child, other family members, and/or members of the social network of the family. It takes a considerable amount of time until positive parenting practices sink in with parents, simply because replacing adverse parenting practices and/or beliefs with positive parenting strategies cannot be expected to occur within a short time period. In general, child maltreatment interventions aim for a *sustained* change in parent--child interactions over time by improving parenting practices and/or beliefs, so that (the recurrence of) child maltreatment is prevented. Therefore, it is important in primary research to thoroughly conduct follow-up evaluations of considerable length, as the true effects of child maltreatment interventions may be particularly expressed in follow-up rather than in post-treatment evaluations.

For curative interventions, a moderating effect was found for type of outcome (smaller effect sizes were found for studies using self-report data obtained from parents compared to studies using official reports). This may be explained by two difficulties that arise when using self-report methods, such as interviews or questionnaires. First, it may be difficult for parents to be honest about the way they raise their children and to admit any neglectful or abusive parenting practices. As a result, parents may give socially desirable answers. Second, parents may be biased toward presenting a more favorable image of their own parenting behavior (see, for instance, Schwarz et al. [@CR162]). Both issues may result in an underestimation of the true number of maltreatment occurrences, which in turn influences the magnitude of effect sizes. On the other hand, it can be assumed that official reports also lead to an underrepresentation of child abuse because researchers found that many occurrences of child maltreatment do not appear in official records (e.g., Fergusson et al. [@CR68]; Finkelhor [@CR70]; MacMillan et al. [@CR122]).

Effective Components {#Sec15}
--------------------

As for intervention duration, we found that preventive interventions with a short duration (up to 6 months) were more effective than preventive interventions of longer duration, whereas for curative interventions, no significant effect of intervention duration was found. This finding is in line with findings of a meta-analysis on effective ingredients of prevention programs for youth at risk for juvenile delinquency, which also showed that preventive interventions of shorter duration were more effective than preventive interventions of longer duration (De Vries et al. [@CR46]). In contrast, Euser et al. ([@CR61]) concluded in their meta-analysis that interventions with an average length (6--12 months) were most effective, but this conclusion seems too strong. There was hardly any absolute difference in mean effect between their 0--6 month category (*d* = .22) and their 6--12 month category (*d* = .23). The "*less is more"* effect in attachment-based interventions found by Bakermans-Kranenburg et al. ([@CR16]) seems also applicable to interventions aimed at reducing or preventing child maltreatment. However, intervention duration was no longer a significant predictor of effect size in the multiple moderator model, which implies that intervention duration does not make a unique contribution to the prediction of effect size above follow-up duration (in months), and whether or not interventions were a parent training intervention, a substance abuse intervention, and focusing on improving parents' self-confidence.

Moreover, it seems to be important to adjust the intensity of an intervention to the level of risk present in a family. In case of high risk, it may be important to intervene intensively, whereas in case of low risk, less intensive interventions are appropriate. This principle is known as the risk principle of the risk--need--responsivity (RNR) model (e.g., Andrews and Bonta [@CR5], [@CR6]; Andrews et al. [@CR7]). This model is widely used for preventing recidivism in the (juvenile) criminal justice system, as various meta-analyses have shown that judicial interventions aimed at behavioral change are most effective when delivered according to this model (Andrews et al. [@CR9]; Andrews and Dowden [@CR8]). It can be assumed that the RNR principles also apply to interventions aimed at preventing or reducing child maltreatment, because child maltreatment, like delinquent behavior, is caused by the accumulation of risk factors in multiple systems (Belsky [@CR21], [@CR22]; Brown et al. [@CR29]). Furthermore, many risk factors of delinquent behavior resemble risk factors for child maltreatment, like poverty, stress in the family, and psychiatric problems of parents, including alcohol or drug problems (Stith et al. [@CR167]).

For preventive interventions, lager effect sizes were found for interventions focusing on increasing self-confidence of parents. For curative interventions, larger effect sizes were found for improving parenting skills, improving personal skills of parents (trend significant), addressing mental health problems of parents (trend significant), providing social and/or emotional support, and improving a child's well-being (trend significant). These findings offer possibilities to improve interventions. For curative interventions, smaller effect sizes were found for interventions focusing on empowerment (trend significant). This finding is in line with studies reporting that children from high-risk families benefit less from the presence of protective factors (e.g., Luthar and Goldstein [@CR119]; Miller et al. [@CR130]; Vanderbilt-Adriance and Shaw [@CR180]), indicating that interventions aimed at increasing or strengthening protective factors in high-risk families do not necessarily lead to a decrease in child maltreatement. Vanderbilt-Adriance and Shaw ([@CR180]) concluded in their review of studies on resilience that in high-risk families, there should be a focus on both strengthening protective factors and reducing risks, because there are limits to the amount of risk that can be mitigated.

Implications for Policy and Clinical Practice {#Sec16}
---------------------------------------------

First, when implementing best practices, clinical professionals and policy makers should opt for interventions that produce the largest effects on preventing or reducing child maltreatment. Cognitive behavioral therapy, home visitation, parent training, family-based/multisystemic, substance abuse, and combined interventions were effective in preventing and/or reducing child maltreatment. Specific individual interventions with a (trend) significant effect on preventing or reducing child maltreatment that were examined in at least two independent studies were: MST-CAN/BSF (intensive family therapy), Triple P (a parent training), ACT-Parent's Raising Safe Kids Program (a short-term parent training), and Healthy Start (a home visitation intervention). Implementing these (types of) interventions in clinical practice may therefore be fruitful.

Second, the effectiveness of existing interventions could be improved by integrating specific components associated with greater effectiveness into interventions, such as focusing on improving parenting skills and providing social and/or emotional support in curative interventions, and increasing self-confidence of parents in preventive interventions. For curative interventions, it seems important to screen for mental health problems in parents and if present, to address these problems in interventions. Interventions targeting substance-abusing parents appeared to be very effective, as well as interventions addressing other mental health problems. Furthermore, improving child well-being and providing social and/or emotional support seems to be effective components of interventions aimed at maltreating families.

Limitations {#Sec17}
-----------

Several limitations need to be discussed. First, a large amount of literature is available on the effectiveness of interventions aimed at preventing or reducing child maltreatment, and therefore, it is possible that we may have missed primary studies. However, we included a rather large number of studies in our meta-analysis (121 independent studies) and this led us to assume that our sample of studies is representative of all studies on the effect of child maltreatment interventions that have been conducted to date. Second, the reported information of the studies included in the meta-analysis was sometimes limited. A relatively large number of studies failed to report important information on intervention characteristics, such as specific intervention practices and delivery techniques.

A third limitation is related to the outcome measure that was assessed in primary studies. In some studies, it is assumed that a report, investigation, or a recurrence in child protection is indicative of abuse or neglect. However, the relationship between contact with the child protection system and maltreatment is not straightforward (Jenkins et al. [@CR96]). Several studies showed that a large proportion of child maltreatment is not reported to child protection authorities (Cyr et al. [@CR41]; Finkelhor et al. [@CR71], [@CR72]). Population-based surveys showed that rates of maltreatment are more than ten times the rates of substantiated maltreatment in those same jurisdictions (e.g., Fergusson et al. [@CR68]; Finkelhor [@CR70]; MacMillan et al. [@CR122]). Further, in many cases reported to child protection authorities, maltreatment is not substantiated.

Fourth, there are several methodological difficulties regarding the trim-and-fill method. The performance of the trim-and-fill method is limited when effect sizes prove to be heterogeneous (Peters et al. [@CR143]; Terrin et al. [@CR175]). In addition, the application of the trim-and-fill method could mean adding and adjusting for nonexistent effect sizes in response to funnel plots that are asymmetrical, simply because of random variation (Egger et al. [@CR59]). Finally, Nakagawa and Santos ([@CR134]) mentioned that this method has originally been designed for meta-analytic reviews in which independence of effect sizes can be assumed. Despite these shortcomings, there is no best method for detecting and handling missing data in meta-analysis, and therefore, the results from the trim and fill method should be interpreted with caution. In the present study, we only used the trim-and-fill method to calculate a "corrected" overall effect. A fifth limitation is that several moderator analyses were based on a rather small number of effect sizes, implying a low statistical power in the moderator analyses. Finally, it should be kept in mind that the present review was mainly based on primary studies that were conducted in Western countries, and in particular the USA. Since countries differ in social and political climate, organization of child welfare health services, and in ethnic and cultural background of clients served by child welfare, it is questionable whether the present results are representative for nonwestern countries.

Despite these limitations, our study provides important knowledge for science and practice. Our findings show that interventions can be effective in preventing or reducing child maltreatment. The results of this meta-analysis can be used to improve existing interventions, for example by integrating effective components in interventions, or by developing new promising interventions comprising of the most effective components.

Appendix 1 {#Sec18}
==========

See Table [7](#Tab7){ref-type="table"}.Table 7Characteristics of included studiesReferences(s)^a^*N* ^b^\#ESName intervention^c^AC childDesign^d^Type of families served^e^Akai et al. ([@CR2])483My baby and me≤ 2QERAndrews et al. ([@CR4])381PCDC≤ 2RCTRAntle et al. ([@CR10])7601Solution-based caseworkNSQEMArancena et al. ([@CR11])901Home visitation program≤ 2RCTRAsscher et al. ([@CR13])1053Home-Start2--5QERBarnet et al. ([@CR17])1471Home visitation program≤ 2RCTRBarnet et al. ([@CR18])631CB home visitation program≤ 2RCTRBarth et al. ([@CR20])602CPEP≤ 2RCTRBarth ([@CR19])1912CPEP≤ 2RCTRBerzin et al. ([@CR23])45--603FGDM2--5RCTR/MBlack et al. ([@CR24])431Home visitation program≤ 2RCTRBouwmeester-Landweer ([@CR26])448--4695Stevig ouderschap \[*Solid Parenting*\]≤ 2RCTRBrayden et al. ([@CR27])2633Prenatal + pediatric health services≤ 2RCTRBritner and Reppucci ([@CR28])5351Parent education program≤ 2QERBrooten et al. ([@CR193])791Home follow-up care≤ 2RCTRBugental et al. ([@CR30])732HS/HS + cognitive component≤ 2RCTRBugental and Schwartz ([@CR31])802HS + cognitive component≤ 2RCTRCasanueva et al. ([@CR32])5881Parenting services6--12QEMCasiro et al. ([@CR33])^f^1001Homemaker services≤ 2RCTRChaffin et al. ([@CR35])1104PCIT/Enhanced PCIT6--12RCTRChaffin et al. ([@CR34])761PCIT2--5RCTRCrampton and Jackson ([@CR39])941FGDMNSQEMCulp et al. ([@CR40])2631CBFRS home visitation≤ 2QEGPDakof et al. ([@CR42])^f^625Engaging moms programNSRCTMDawe and Harnett ([@CR44])41--422Brief parenting skills training/PUP2--5RCTRDawson et al. ([@CR45])1111Parent support home visits + parent groups≤ 2QERDew and Breakey ([@CR47])44661Hawaii's HS program≤ 2QERDonohue et al. ([@CR48])724Family behavior therapy2--5RCTMDubowitz et al. ([@CR49])5584SEEK6--12RCTRDubowitz et al. ([@CR50])894--11193SEEK6--12QEGPDuggan et al. ([@CR52])5417Hawaii HS programNSRCTRDuggan et al. ([@CR51])249--2977HF Alaska≤ 2RCTRDuMont et al. ([@CR54])\
(2) DuMont et al. ([@CR53])104--117310HF New York≤ 2RCTR/MEasterbrooks et al. ([@CR58])5122HF Massachusetts≤ 2RCTRFalconer et al. ([@CR62])1045--11472HF Florida≤ 2QERFennell and Fishel ([@CR64])18STEP6--12RCTMFergusson et al. ([@CR67])\
(2) Fergusson et al. ([@CR66])370--3914Early start program≤ 2RCTRFraser et al. ([@CR73])\
(2) Armstrong and Morris ([@CR12])124--1602Home visitation program≤ 2RCTRFujiwara et al. ([@CR74])1151Group Triple P6--12QERGalanter et al. ([@CR75])631PCIT6--12QERGershater-Molko et al. ([@CR77])821Project SafeCare2--5QEMGessner ([@CR78])20131HF Alaska≤ 2QERGray et al. ([@CR80])502Pediatric intervention≤ 2RCTRGreen t al. ([@CR81])1081Early head start2--5RCTRGreen et al. ([@CR82])7631HF Oregon≤ 2RCTRGuterman et al. ([@CR84])1014Parent aide services6--12RCTRGuthrie et al. ([@CR85])^f^721Touchpoints training + home visiting≤ 2QERHans et al. ([@CR86])2211Community doula support≤ 2RCTRHarden et al. ([@CR87])5311Early head start≤ 2RCTRHarder ([@CR88])134--1584Parent aide program2--5QEMHardy and Streett ([@CR89])2631Children and youth program≤ 2RCTRHonig and Morin ([@CR90])49--652TPBP≤ 2QERHurlburt et al. ([@CR92])75--3034Incredible years2--5RCTRHuxley and Warner ([@CR93])401Community infant project≤ 2QERJacobs et al. ([@CR94])5942HF Massachusetts≤ 2RCTRJavier et al. ([@CR95])^f^241Incredible years School Age6--12RCTRJohnston et al. ([@CR97])2072Healthy steps/healthy steps + prepare≤ 2QEGPJones Harden ([@CR98])927--9482Early head start≤ 2RCTRJouriles et al. ([@CR100])354Project support6--12RCTMKagitcibasi et al. ([@CR101])217--2252TEEP2--5RCTRKan and Feinberg ([@CR102])1691Family foundations program≤ 2RCTRKirk and Griffith ([@CR103])515--50062Intensive FPSNSQERKnox et al. ([@CR106])923ACT-raising safe Kids2--5QERKnox et al. ([@CR105])841ACT-raising safe kids2--5RCTRKolko ([@CR107])27--3056CBT/family therapy6--12RCTMLam et al. ([@CR108])^f^2018PSBCT6--12RCTMLarson ([@CR109])631Home visits≤ 2QERLealman et al. ([@CR111])302--3122Prevention program≤ 2QERLeCroy and Krysik ([@CR112])1682HF Arizona≤ 2RCTRLeijten et al. ([@CR113])782PCTT≥ 12RCTRLetarte et al. ([@CR114])352Incredible years6--12QEMLinares et al. ([@CR115])99--1082Incredible years6--12RCTMLove et al. ([@CR117])459--9323Early head start≤ 2RCTRLowell et al. ([@CR118])1574Child First≤ 2RCTRLutzker and Rice ([@CR120])971Project 12-ways≤ 2QEMMacMillan et al. ([@CR123])1636Home visitation program6--12RCTMMarcenko and Spence ([@CR124])\
(2) Marcenko et al. ([@CR125])187--1972Prevention program≤ 2RCTRMcKelvey et al. ([@CR127])2271Thrive program≤ 2QERMejdoubi et al. ([@CR128])3321NFP≤ 2RCTRMinkovitz et al. ([@CR131])\
(2) Minkovitz et al. ([@CR132])1308--21448HSYC2--5RCT/QEGPNorr et al. ([@CR135])154--4773REACH-Futures≤ 2RCTROlds et al. ([@CR137])\
(2) Olds et al. ([@CR138])\
(3) Olds et al. ([@CR136])204--2566NFP≤ 2RCTROveisi et al. ([@CR139])2241SOS helps6--12RCTGPParadis et al. ([@CR140])2151Building healthy children≤ 2RCTRPataki and Johnson ([@CR141])11575HF New York≤ 2RCTRPennell and Burford ([@CR142])632FGDMNSQEMPeterson et al. ([@CR144])9947-level parenting model2--5QERPortwood et al. ([@CR146])156--2072ACT-raising safe kidsNSRCTRPosthumus et al. ([@CR147])1326Incredible years2--5QERPuffer et al. ([@CR148])2701PMD2--5RCTRReynolds and Robertson ([@CR149])14081CPC program6--12QERRodrigo et al. ([@CR150])2902Apoyo personal y familiarNSQERRodriguez et al. ([@CR151])5224HF New York≤ 2RCTRRunyon et al. ([@CR154])602Parent--child CBT6--12RCTMSanders et al. ([@CR156])744Enhanced Triple P2--5RCTRSanders et al. ([@CR155])1044Triple P online2--5RCTRSawasdipanich et al. ([@CR157])1162Cognitive adjustment program6--12RCTRSchaeffer et al. ([@CR158])^f^432MST-BSF6--12QEMSchilling et al. ([@CR159])^f^1201PriCARE2--5RCTRScholer et al. ([@CR160])641Play nicely program2--5RCTGPSchuler et al. ([@CR161])\
(2) Nair et al. ([@CR133])161--1711Home intervention≤ 2RCTRShapiro et al. ([@CR163])38--459SSTP≤ 2RCTRSiegel et al. ([@CR164])99--1191Hospital + home support≤ 2RCTRSilovsky et al. ([@CR165])1053SafeCare2--5RCTRStevens-Simon et al. ([@CR166])1271CAMP home visitation program≤ 2RCTRSuess et al. ([@CR169])731STEEP≤ 2QERSundell and Vinnerljung ([@CR170])2392FGC6--12QEMSwenson et al. ([@CR172])868MST-CAN≥ 12RCTMSzykula and Fleischman ([@CR173])481Social learning treatment6--12RCTMThomas and Zimmer-Gembeck ([@CR176])\
(2) Thomas and Zimmer‐Gembeck (Thomas and Zimmer-Gembeck [@CR177])76--1984PCIT2--5RCTMVelasques et al. ([@CR181])551Special families care project≤ 2QERWagner and Clayton ([@CR183])311--3122Teen PAT/Teen PAT + CM≤ 2RCTRWagner et al. ([@CR184])78--1392PAT≤ 2RCTGP/RWalton ([@CR185])1371IFPS6--12RCTMWalton ([@CR186])2081IFPS6--12RCTMWalton et al. ([@CR187])1103Family reunification services6--12RCTMWeigensberg et al. ([@CR188])6501FGDM2--5QEMWesch and Lutzker ([@CR189])4641Project 12-ways≤ 2QEMWolfe et al. ([@CR190])301Parenting training2--5QERWood et al. ([@CR191])1081Homebuilders6--12QEMZhai et al. ([@CR192])28075Head Start≤ 2QER*Pub. year* Publication year, *N* total sample size, \#*ES* amount of effect sizes, *AC child* age category of the child at the start of the program, *Design* research design, *PCDC* parent child development centers, *CB* community-based, *CPEP* child--parent enrichment project, *FGDM* family group decision making, *HS* healthy start, *PCIT* parent--child interaction therapy, *CBFRS* community-based family resource service, *PUP* parents under pressure, *SEEK* safe environment for every kid, *HF* healthy families, *STEP* systematic training for effective parenting, *TPBP* teen parents and babies program, *TEEP* Turkish early enrichment project, *IFPS* intensive family preservation services, *ACT* adults and children together, *CBT* cognitive behavioral therapy, *PSBCT* parent skills with behavioral couples therapy, *PCTT* parents and children talking together, *FIRST* family information, referral and support team, *NFP* nurse family partnership, *HSYC* healthy steps for young children, *REACH* resources, education and care in the home, *PMD* parents make the difference, *CPC* child--parent center, *MST*-*BSF* multisystemic therapy---building stronger families, *PriCARE* primary child--adult relationship enhancement, *SSTP* stepping stones Triple P, *CAMP* Colorado adolescent maternity program, *STEEP* steps toward effective and enjoyable parenting, *FGC* family group conferences, *MST*-*CAN* multisystemic therapy for child abuse and neglect, *PAT* parent as teachers, *CM* case management, *CPS* child protective services, *NS* not specified, *QE* quasi-experimental, *RCT* randomized controlled trial, *R* risk group, *GP* general population, *M* maltreating parents^a^When secondary or tertiary literature was available (studies making use of the same sample), this is indicated by '(2)' or '(3)'^b^When more than one sample size was present within a study (varied by effect size), the range was displayed (minimum N--maximum N)^c^When more than one program was examined within a study, this was indicated by a slash (/) in between the different program names^d^When more than one research design was used within a study, this was indicated by a slash (/) in between the different research designs^e^When more than one type of sample was present within a study, this was indicated by a slash (/) in between the different types of samples^f^Feasibility/pilot study

This work was supported by a grant from ZonMw, the Netherlands Organization for Health Research and Development (Grant Number 74110.0001).

Conflict of interest {#FPar1}
====================

None of the authors of this review have any conflicts of interest to declare.

Ethical Approval {#FPar2}
================

This research did not involve human subjects, it did not require consent or assent forms that needed approval by an ethics committee.
