Service-level interventions to reduce waiting time in outpatient and community health settings may be sustained: a systematic review
Service-level interventions in community health and outpatient clinics can reduce waiting, but evaluations do not often report on the sustainability of outcomes. 

This review suggests interventions that embed changes to referral management processes and/or models of care can lead to sustained improvements in timely access. Existing evidence provides examples of strategies that have been successful in sustained reductions in waiting time in community and outpatient services that could provide initial guidance for service providers addressing long wait times. 

From a large body of evidence of over 150 000 patients/clients, there is low to very low certainty evidence that service-level interventions can lead to sustained reductions in waiting time. Further high-quality research would better inform service providers about what interventions are most effective and provide the greatest return on investment 

Timely access to health services is vital for efficient and effective delivery of care in outpatient and community settings. For patients, receiving the right service at the right time reduces the impacts of health conditions and improves the quality of life. With increasing demand and inefficiencies in service delivery, however, many patients accessing healthcare in these settings experience long wait times. Factors increasing demand include an ageing population, increased chronic conditions and an increasing population, while supply is impacted by reduced workforce capacity and resource constraints. Research suggests that service-level strategies can reduce wait time for health services but are often measured over a short period, raising questions about long-term sustainability. Interventions to address waiting time for health services can involve changes at the policy level (such as funding incentives), service level (such as organisational policy or model of care changes) or patient/clinician behaviour (through choices regarding attendance, referrals or individual treatment). At the service level, a range of different strategies have been used to categorise waiting time interventions in outpatient and community settings. For example, a systematic review evaluating interventions to reduce wait times in paediatric outpatient and community services identified three broad categories of strategies to reduce wait times in health services, described as rapid access (streamlining access to an initial assessment appointment), process efficiencies (activities to improve workflow and reduce waste) or substitution (workforce innovations to use less specialised staff in advanced scope roles). Other authors have categorised waiting time interventions using terms, such as resource realignment, operational efficiency and process improvement, or according to stages of the patient journey, such as those focusing on referral management versus models of care. Variation in the description of waiting list interventions may reflect diversity in the strategies that have been used across different healthcare settings. The low quality of the research in this field has been identified as a limitation in all these reviews, but all report consistent findings that different types of service-level interventions can reduce waitlists and wait times in outpatient and community settings. While two reviews reported on follow-up periods of the included studies, none addressed the issue of sustainability of reducing waiting time during analysis. Studies evaluating waiting time interventions often report relatively short follow-up periods, raising questions about long-term sustainability. Sustainability has been defined as ‘the ongoing delivery of health programmes, which may be measured by the longevity of independent projects, or how well programmes become institutionalised in organisations or health and social systems’ (Braithwaite, 2017, p. 1580). Evidence from several systematic reviews suggests that health service interventions, in general, are more likely to be sustained when supported by strong leadership, sufficient resources and adequate planning for sustainability, and when specific barriers, facilitators and necessary adaptations of the intervention to the service are considered. Klaic et al recognised the level to which a new intervention is integrated into an organisation’s service setting and subsystems, described as penetration, and also has a strong impact on the sustainability of the intervention. An intervention with successful penetration no longer requires active monitoring, which supports the likelihood of sustainability once any initial supports and/or funding have ceased. While several systematic reviews provide insights into factors associated with the sustainability of health service interventions, in general, no reviews to date have explored the sustainability of interventions to reduce waiting times. The primary aim of this systematic review was, therefore, to determine whether interventions implemented at the service level to reduce wait times in outpatient and community health services can be sustained. The secondary aim was to describe the features of wait time interventions and the settings in which they have been implemented that are associated with sustainability. 

This systematic review was registered prospectively with PROSPERO CRD 42022346200 (23/7/2022) and is reported consistent with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis. Consumer involvement: The topic for this systematic review has been informed by our previous qualitative work with consumers waiting for healthcare. Consumers told us that delays in access to services have an impact on health outcomes, as well as causing distress and anxiety, and that sustainable reduction of healthcare waiting lists is a high priority for health systems. Consumers were not directly involved in the design of the protocol or conduct of this review. Search strategy A search strategy was designed to identify studies that evaluated the sustainability of service-level interventions in healthcare organisations to reduce wait times. Electronic databases CINAHL, Medline, Embase and Psych Info were searched from the earliest available date to August 2022. The search strategy combined the key concepts of outpatient health services, waiting and sustainability. Synonyms for each concept (eg, ambulatory, outpatient and community health; waiting list, waiting time and timely access; and sustainability, maintenance and continuation) were combined with ‘OR’ with results between concepts combined with ‘AND’. Full search strategies can be seen in . The citations and references list for included studies were manually checked to identify further studies that met the inclusion criteria that may have been missed in database searching. Inclusion and exclusion criteria Any intervention implemented at the service level for the purpose of reducing wait time from referral to initial appointment for assessment and commencement of treatment with a service or reducing the number of people on waiting lists for care was eligible for inclusion, including but not limited to process improvements, changes to models of care (such as use of telehealth or group interventions), workforce adjustments or referral processing systems. For the purpose of this review, sustainability was measured as maintenance of improvements for at least 12 months following the implementation of an intervention or service change. Any study design was, therefore, included, provided a quantitative waiting outcome (eg, mean/median waiting times or number of referrals on the waitlist) that was reported a minimum of three times (preintervention, postintervention and at a minimum of 12 months follow-up). This systematic review included any health service delivered in an outpatient or community setting, including but not limited to diagnostic services, allied health services, medical outpatient clinics, primary care or mental health clinics. Studies were excluded if they described interventions to reduce wait times for surgery (including organ transplant), emergency services (including ambulance arrival and hospital emergency departments), inpatient hospital care, school-based services or were not in English. Article selection and data extraction All potentially eligible studies were imported into review software, Covidence, and duplicate references deleted. A review of the titles and abstracts was conducted by two reviewers independently to determine whether studies met the inclusion criteria. Studies that did not meet the inclusion criteria were excluded. Discrepancies were resolved through discussion between reviewers, and full-text manuscripts were obtained where doubt persisted. Studies that met inclusion criteria based on title/abstract screening were subject to a full-text review by two reviewers, independently. When discrepancies arose, they were discussed between the reviewers. If the reviewers did not agree on an outcome, an additional reviewer was consulted. Data were extracted from all studies using a predesigned data extraction table that included the study characteristics, research design, setting, details of intervention, outcomes measured, baseline measurement, postintervention measurement, follow-up measurement and the key sustainability findings. Data extraction was completed by two reviewers independently. Risk of bias Methodological quality was evaluated using the mixed-methods appraisal tool (MMAT). The MMAT provides checklists for researchers to critically review the methodological quality of qualitative research, randomised controlled trials, non-randomised studies, quantitative descriptive studies and mixed-methods studies. Adapted to each study design, five questions are asked to critique the methodological quality of each paper. Two researchers independently assessed the methodological quality for each included paper, with any discrepancies discussed until a consensus was achieved. A third researcher was available for consultation if consensus could not be achieved. Analysis A deductive narrative synthesis was conducted to group the included papers by intervention strategy. Three researchers (KM, KEH and AL) independently assigned interventions into categories. Reviewers then discussed their findings with any disagreements resolved by discussion until consensus was achieved. The primary outcome was the sustainability of results following the implementation of service-level interventions to reduce wait times. Given the lack of guidance on a definition of sustainability for waiting time interventions in the literature, a classification system was developed for the purpose of this review based on a pragmatic judgement of clinical significance. The level of sustainability of each study was judged as ‘sustained’ (wait time/waitlist has reduced from baseline to postintervention and remained below postintervention levels at follow-up), ‘partially sustained’ (indicated by small increases in waiting time at follow-up of <10% or inconsistent results across subgroups or outcome measures) or ‘not sustained’ (wait times/waitlist increased by>10% at follow-up compared with postintervention levels). We then applied the Grading of Recommendation, Assessment, Development and Evaluation (GRADE) to all studies within each of the intervention types to analyse the certainty of evidence, adapted for studies without a single estimate of effect. For each outcome, the GRADE domains (methodological limitations of the studies, directness of the evidence, precision of estimates, consistency of the evidence and the likelihood of publication bias) were rated as not serious, borderline or serious ( ). Overall assessment of the strength of the evidence for each outcome was judged to be high, moderate, low or very low. Strength of evidence from observational studies was initially assessed as being low, with potential for upgrade (due to magnitude of effect) or downgrade (due to at least one serious concern or two or more borderline concerns among the five GRADE domains). 

A search strategy was designed to identify studies that evaluated the sustainability of service-level interventions in healthcare organisations to reduce wait times. Electronic databases CINAHL, Medline, Embase and Psych Info were searched from the earliest available date to August 2022. The search strategy combined the key concepts of outpatient health services, waiting and sustainability. Synonyms for each concept (eg, ambulatory, outpatient and community health; waiting list, waiting time and timely access; and sustainability, maintenance and continuation) were combined with ‘OR’ with results between concepts combined with ‘AND’. Full search strategies can be seen in . The citations and references list for included studies were manually checked to identify further studies that met the inclusion criteria that may have been missed in database searching. 

Any intervention implemented at the service level for the purpose of reducing wait time from referral to initial appointment for assessment and commencement of treatment with a service or reducing the number of people on waiting lists for care was eligible for inclusion, including but not limited to process improvements, changes to models of care (such as use of telehealth or group interventions), workforce adjustments or referral processing systems. For the purpose of this review, sustainability was measured as maintenance of improvements for at least 12 months following the implementation of an intervention or service change. Any study design was, therefore, included, provided a quantitative waiting outcome (eg, mean/median waiting times or number of referrals on the waitlist) that was reported a minimum of three times (preintervention, postintervention and at a minimum of 12 months follow-up). This systematic review included any health service delivered in an outpatient or community setting, including but not limited to diagnostic services, allied health services, medical outpatient clinics, primary care or mental health clinics. Studies were excluded if they described interventions to reduce wait times for surgery (including organ transplant), emergency services (including ambulance arrival and hospital emergency departments), inpatient hospital care, school-based services or were not in English. 

All potentially eligible studies were imported into review software, Covidence, and duplicate references deleted. A review of the titles and abstracts was conducted by two reviewers independently to determine whether studies met the inclusion criteria. Studies that did not meet the inclusion criteria were excluded. Discrepancies were resolved through discussion between reviewers, and full-text manuscripts were obtained where doubt persisted. Studies that met inclusion criteria based on title/abstract screening were subject to a full-text review by two reviewers, independently. When discrepancies arose, they were discussed between the reviewers. If the reviewers did not agree on an outcome, an additional reviewer was consulted. Data were extracted from all studies using a predesigned data extraction table that included the study characteristics, research design, setting, details of intervention, outcomes measured, baseline measurement, postintervention measurement, follow-up measurement and the key sustainability findings. Data extraction was completed by two reviewers independently. 

Methodological quality was evaluated using the mixed-methods appraisal tool (MMAT). The MMAT provides checklists for researchers to critically review the methodological quality of qualitative research, randomised controlled trials, non-randomised studies, quantitative descriptive studies and mixed-methods studies. Adapted to each study design, five questions are asked to critique the methodological quality of each paper. Two researchers independently assessed the methodological quality for each included paper, with any discrepancies discussed until a consensus was achieved. A third researcher was available for consultation if consensus could not be achieved. 

A deductive narrative synthesis was conducted to group the included papers by intervention strategy. Three researchers (KM, KEH and AL) independently assigned interventions into categories. Reviewers then discussed their findings with any disagreements resolved by discussion until consensus was achieved. The primary outcome was the sustainability of results following the implementation of service-level interventions to reduce wait times. Given the lack of guidance on a definition of sustainability for waiting time interventions in the literature, a classification system was developed for the purpose of this review based on a pragmatic judgement of clinical significance. The level of sustainability of each study was judged as ‘sustained’ (wait time/waitlist has reduced from baseline to postintervention and remained below postintervention levels at follow-up), ‘partially sustained’ (indicated by small increases in waiting time at follow-up of <10% or inconsistent results across subgroups or outcome measures) or ‘not sustained’ (wait times/waitlist increased by>10% at follow-up compared with postintervention levels). We then applied the Grading of Recommendation, Assessment, Development and Evaluation (GRADE) to all studies within each of the intervention types to analyse the certainty of evidence, adapted for studies without a single estimate of effect. For each outcome, the GRADE domains (methodological limitations of the studies, directness of the evidence, precision of estimates, consistency of the evidence and the likelihood of publication bias) were rated as not serious, borderline or serious ( ). Overall assessment of the strength of the evidence for each outcome was judged to be high, moderate, low or very low. Strength of evidence from observational studies was initially assessed as being low, with potential for upgrade (due to magnitude of effect) or downgrade (due to at least one serious concern or two or more borderline concerns among the five GRADE domains). 

Yield The search of databases identified 7770 papers after removal of duplicates ( ). 82 papers were retained for full-text review. A further 60 papers were excluded during the full-text review with the most common reasons being wrong publication type (n=16), less than 12 month follow-up (n=13) and wrong outcomes (n=11), yielding 22 papers for inclusion. Study characteristics The 22 studies included in this review were conducted in the UK (n=5), Canada (n=5), USA (n=5), Sweden (n=2), Australia (n=2), Spain (n=1), Netherlands (n=1) and New Zealand (n=1). Ten were set in outpatient specialist clinics, four in mental health clinics and four allied health clinics, three in MRI services and one in an adolescent medicine clinic. Population numbers were not reported consistently with seven papers providing no indication of the sample size in their research. The population numbers reported across the 22 studies were approximately 200 000, although reporting was inconsistent. Characteristics of all included studies are summarised in . There were no randomised trials. All studies were historically controlled, providing data collected during periods before and after the intervention either using simple, uncontrolled pre–post designs, controlled before and after studies or interrupted time series. Five studies conducted time-series analyses. 17 studies implemented their intervention at a single site. Four studies introduced the intervention across multiple sites and one had a comparison site. There were insufficient data across the studies to formally explore the likelihood of publication bias using funnel plots. 18 studies collected observations continuously over regular time periods. Three measured outcomes at weekly intervals, seven at monthly intervals, four at quarterly intervals and four used annual observations. The remaining four studies used repeated measures at key time points, which typically included baseline, postintervention and follow-up. The follow-up period varied from 18 months to 7 years. The most common time measurement was 2 years postintervention (n=7 studies), followed by 5 years (n=5). Risk of bias Overall, six studies met all five MMAT criteria. Less than half of the studies described the target population. The outcome measures and the intervention were sufficiently described in 21 of the 22 studies. 13 studies were rated as having complete outcome data with insufficient information to assess this in 9 studies. Confounders were accounted for in 8 of the studies and 16 of the studies reported enough information for the reviewers to ascertain if the intervention was implemented as intended. Full details of the MMAT ratings for all studies can be found in the . Study findings After conducting a deductive thematic analysis, the interventions in the included papers were grouped into three categories: referral entry, open access and substitution, used either as stand-alone interventions or in combination ( ). Referral entry interventions targeted the process from entry to acceptance of a referral within an organisation and encompassed interventions that developed or improved triage systems, such as the use of e-referrals and centralised intake systems. Open access interventions involved preserving space for new appointments based on demand, including systems, such as advanced access, the choice and partnership approach and the Specific Timely Assessment for Triage (STAT) model that are based on this principle. Substitution involved training less specialised workers to perform aspects of care usually conducted by those with a higher level of training, such as the use of nurse practitioners, allied health staff or more junior medical staff to complete tasks historically completed by medical specialists. 14 studies were considered to have used interventions within a single category, and 8 used a combination of intervention types. Most incorporated additional process efficiency measures, but these were integrated within these broader categories and were, therefore, not considered as a stand-alone category. While some studies accessed short-term resources dedicated to supporting the implementation of an intervention, all interventions were presented as ongoing changes to the service; no studies described time-limited interventions, such as temporary increase in supply to address backlog. Referral entry interventions There was low certainty evidence from six studies that reduced wait times achieved from referral entry interventions were sustained over time ( ). Referral entry interventions were used in mental health services (n=1), a service for HIV-infected youth (n=1), medical resonance imaging clinic (n=1), urology clinic (n=1), cardiology service (n=1) and an outpatient rheumatology clinic (n=1). Miller et al changed referral screening and intake processes in an HIV clinic, with sustained improvements in linkage and waiting times reduced by more than two-thirds. Interventions introduced by Bhullar et al and Hankinson et al focused on grouping like services and reducing variability of intervention types, with wait times reduced by more than two-thirds and maintained at 2 and 4 years, respectively. Two studies reported implementing a centralised system for intake and triage, finding the quality of referrals improved and wait times were managed more effectively, although only one of these was able to achieve and maintain reduced waiting times. Overall, five of the six studies saw a reduction in wait times after the minimum 1-year post intervention follow-up of which four had large enough effect sizes to upgrade the rating of certainty of the evidence by one GRADE level. Open access interventions There was low certainty evidence of sustained reductions in wait times from six studies following the introduction of open access interventions ( ). These studies were implemented in allied health clinics (n=3), an outpatient specialist clinic (n=1), a urology clinic (n=1) and an MRI clinic (n=1). All studies clearly reported implementing open/advanced access strategies with three stating the relevance of understanding the supply and demand for each service as important to their intervention. Four studies were classified as demonstrating sustained improvements, with three describing wait reductions of more than two-thirds and one demonstrating a significantly reducing trend in waiting time on an interrupted time-series analysis. Speed and Fyfe were able to reduce waiting variability but not waiting time over the 2 years of their trial in an occupational therapy service, and one open access trial in medical outpatient clinics was judged as being partially sustained due to improvements being maintained at 10 of 14 trial sites. Substitution There was low certainty of evidence from two studies that substitution strategies sustained reduced wait times ( ). Of these, one study achieved a high methodological quality meeting all criteria on the MMAT and the second had low methodological quality meeting only two criteria. Both studies reported that a substitution-only intervention achieved sustained reductions to wait times. One study described a mean wait time reduction from 169 to 48 days in an allied health clinic after implementing a strategy in which an advanced allied health practitioner assessed new referrals. The remaining study reported a reduction in wait times at an outpatient specialist clinic from 9 days to 2.5 after upskilling support workers to complete tasks that were, otherwise, completed by the specialist nurses. Combined interventions There was very low certainty evidence that combined interventions sustained wait times ( ). Eight studies introduced combined interventions that included elements from both referral entry and open access and two studies combined all three intervention types. The combination of these intervention types typically aimed to create new processes for ensuring that appropriate referrals were accepted into the service, triaged and provided appointments to the most appropriate service in a timely manner. Seven of the eight studies were considered to have sustained reduced wait times, often with very large effect sizes; all reduced and maintained waiting times or the number of people on the waiting list at less than 50% of preintervention levels, and three reduced wait times by more than 90% over 5 years. One study was considered partially sustained due to maintained improvements in the number of people on the waiting list, but reported limited effect for waiting time. 

The search of databases identified 7770 papers after removal of duplicates ( ). 82 papers were retained for full-text review. A further 60 papers were excluded during the full-text review with the most common reasons being wrong publication type (n=16), less than 12 month follow-up (n=13) and wrong outcomes (n=11), yielding 22 papers for inclusion. 

The 22 studies included in this review were conducted in the UK (n=5), Canada (n=5), USA (n=5), Sweden (n=2), Australia (n=2), Spain (n=1), Netherlands (n=1) and New Zealand (n=1). Ten were set in outpatient specialist clinics, four in mental health clinics and four allied health clinics, three in MRI services and one in an adolescent medicine clinic. Population numbers were not reported consistently with seven papers providing no indication of the sample size in their research. The population numbers reported across the 22 studies were approximately 200 000, although reporting was inconsistent. Characteristics of all included studies are summarised in . There were no randomised trials. All studies were historically controlled, providing data collected during periods before and after the intervention either using simple, uncontrolled pre–post designs, controlled before and after studies or interrupted time series. Five studies conducted time-series analyses. 17 studies implemented their intervention at a single site. Four studies introduced the intervention across multiple sites and one had a comparison site. There were insufficient data across the studies to formally explore the likelihood of publication bias using funnel plots. 18 studies collected observations continuously over regular time periods. Three measured outcomes at weekly intervals, seven at monthly intervals, four at quarterly intervals and four used annual observations. The remaining four studies used repeated measures at key time points, which typically included baseline, postintervention and follow-up. The follow-up period varied from 18 months to 7 years. The most common time measurement was 2 years postintervention (n=7 studies), followed by 5 years (n=5). 

Overall, six studies met all five MMAT criteria. Less than half of the studies described the target population. The outcome measures and the intervention were sufficiently described in 21 of the 22 studies. 13 studies were rated as having complete outcome data with insufficient information to assess this in 9 studies. Confounders were accounted for in 8 of the studies and 16 of the studies reported enough information for the reviewers to ascertain if the intervention was implemented as intended. Full details of the MMAT ratings for all studies can be found in the . 

After conducting a deductive thematic analysis, the interventions in the included papers were grouped into three categories: referral entry, open access and substitution, used either as stand-alone interventions or in combination ( ). Referral entry interventions targeted the process from entry to acceptance of a referral within an organisation and encompassed interventions that developed or improved triage systems, such as the use of e-referrals and centralised intake systems. Open access interventions involved preserving space for new appointments based on demand, including systems, such as advanced access, the choice and partnership approach and the Specific Timely Assessment for Triage (STAT) model that are based on this principle. Substitution involved training less specialised workers to perform aspects of care usually conducted by those with a higher level of training, such as the use of nurse practitioners, allied health staff or more junior medical staff to complete tasks historically completed by medical specialists. 14 studies were considered to have used interventions within a single category, and 8 used a combination of intervention types. Most incorporated additional process efficiency measures, but these were integrated within these broader categories and were, therefore, not considered as a stand-alone category. While some studies accessed short-term resources dedicated to supporting the implementation of an intervention, all interventions were presented as ongoing changes to the service; no studies described time-limited interventions, such as temporary increase in supply to address backlog. Referral entry interventions There was low certainty evidence from six studies that reduced wait times achieved from referral entry interventions were sustained over time ( ). Referral entry interventions were used in mental health services (n=1), a service for HIV-infected youth (n=1), medical resonance imaging clinic (n=1), urology clinic (n=1), cardiology service (n=1) and an outpatient rheumatology clinic (n=1). Miller et al changed referral screening and intake processes in an HIV clinic, with sustained improvements in linkage and waiting times reduced by more than two-thirds. Interventions introduced by Bhullar et al and Hankinson et al focused on grouping like services and reducing variability of intervention types, with wait times reduced by more than two-thirds and maintained at 2 and 4 years, respectively. Two studies reported implementing a centralised system for intake and triage, finding the quality of referrals improved and wait times were managed more effectively, although only one of these was able to achieve and maintain reduced waiting times. Overall, five of the six studies saw a reduction in wait times after the minimum 1-year post intervention follow-up of which four had large enough effect sizes to upgrade the rating of certainty of the evidence by one GRADE level. Open access interventions There was low certainty evidence of sustained reductions in wait times from six studies following the introduction of open access interventions ( ). These studies were implemented in allied health clinics (n=3), an outpatient specialist clinic (n=1), a urology clinic (n=1) and an MRI clinic (n=1). All studies clearly reported implementing open/advanced access strategies with three stating the relevance of understanding the supply and demand for each service as important to their intervention. Four studies were classified as demonstrating sustained improvements, with three describing wait reductions of more than two-thirds and one demonstrating a significantly reducing trend in waiting time on an interrupted time-series analysis. Speed and Fyfe were able to reduce waiting variability but not waiting time over the 2 years of their trial in an occupational therapy service, and one open access trial in medical outpatient clinics was judged as being partially sustained due to improvements being maintained at 10 of 14 trial sites. Substitution There was low certainty of evidence from two studies that substitution strategies sustained reduced wait times ( ). Of these, one study achieved a high methodological quality meeting all criteria on the MMAT and the second had low methodological quality meeting only two criteria. Both studies reported that a substitution-only intervention achieved sustained reductions to wait times. One study described a mean wait time reduction from 169 to 48 days in an allied health clinic after implementing a strategy in which an advanced allied health practitioner assessed new referrals. The remaining study reported a reduction in wait times at an outpatient specialist clinic from 9 days to 2.5 after upskilling support workers to complete tasks that were, otherwise, completed by the specialist nurses. Combined interventions There was very low certainty evidence that combined interventions sustained wait times ( ). Eight studies introduced combined interventions that included elements from both referral entry and open access and two studies combined all three intervention types. The combination of these intervention types typically aimed to create new processes for ensuring that appropriate referrals were accepted into the service, triaged and provided appointments to the most appropriate service in a timely manner. Seven of the eight studies were considered to have sustained reduced wait times, often with very large effect sizes; all reduced and maintained waiting times or the number of people on the waiting list at less than 50% of preintervention levels, and three reduced wait times by more than 90% over 5 years. One study was considered partially sustained due to maintained improvements in the number of people on the waiting list, but reported limited effect for waiting time. 

There was low certainty evidence from six studies that reduced wait times achieved from referral entry interventions were sustained over time ( ). Referral entry interventions were used in mental health services (n=1), a service for HIV-infected youth (n=1), medical resonance imaging clinic (n=1), urology clinic (n=1), cardiology service (n=1) and an outpatient rheumatology clinic (n=1). Miller et al changed referral screening and intake processes in an HIV clinic, with sustained improvements in linkage and waiting times reduced by more than two-thirds. Interventions introduced by Bhullar et al and Hankinson et al focused on grouping like services and reducing variability of intervention types, with wait times reduced by more than two-thirds and maintained at 2 and 4 years, respectively. Two studies reported implementing a centralised system for intake and triage, finding the quality of referrals improved and wait times were managed more effectively, although only one of these was able to achieve and maintain reduced waiting times. Overall, five of the six studies saw a reduction in wait times after the minimum 1-year post intervention follow-up of which four had large enough effect sizes to upgrade the rating of certainty of the evidence by one GRADE level. 

There was low certainty evidence of sustained reductions in wait times from six studies following the introduction of open access interventions ( ). These studies were implemented in allied health clinics (n=3), an outpatient specialist clinic (n=1), a urology clinic (n=1) and an MRI clinic (n=1). All studies clearly reported implementing open/advanced access strategies with three stating the relevance of understanding the supply and demand for each service as important to their intervention. Four studies were classified as demonstrating sustained improvements, with three describing wait reductions of more than two-thirds and one demonstrating a significantly reducing trend in waiting time on an interrupted time-series analysis. Speed and Fyfe were able to reduce waiting variability but not waiting time over the 2 years of their trial in an occupational therapy service, and one open access trial in medical outpatient clinics was judged as being partially sustained due to improvements being maintained at 10 of 14 trial sites. 

There was low certainty of evidence from two studies that substitution strategies sustained reduced wait times ( ). Of these, one study achieved a high methodological quality meeting all criteria on the MMAT and the second had low methodological quality meeting only two criteria. Both studies reported that a substitution-only intervention achieved sustained reductions to wait times. One study described a mean wait time reduction from 169 to 48 days in an allied health clinic after implementing a strategy in which an advanced allied health practitioner assessed new referrals. The remaining study reported a reduction in wait times at an outpatient specialist clinic from 9 days to 2.5 after upskilling support workers to complete tasks that were, otherwise, completed by the specialist nurses. 

There was very low certainty evidence that combined interventions sustained wait times ( ). Eight studies introduced combined interventions that included elements from both referral entry and open access and two studies combined all three intervention types. The combination of these intervention types typically aimed to create new processes for ensuring that appropriate referrals were accepted into the service, triaged and provided appointments to the most appropriate service in a timely manner. Seven of the eight studies were considered to have sustained reduced wait times, often with very large effect sizes; all reduced and maintained waiting times or the number of people on the waiting list at less than 50% of preintervention levels, and three reduced wait times by more than 90% over 5 years. One study was considered partially sustained due to maintained improvements in the number of people on the waiting list, but reported limited effect for waiting time. 

This review of 22 studies investigated the sustainability of service-level interventions delivered to over 150 000 people to reduce wait times in outpatient and community health settings. Overall, we found low to very low certainty evidence that referral entry, open access and substitution interventions implemented either alone or in combination were effective in sustaining reductions in waiting in outpatient and community health services. Most studies introduced a range of general process efficiencies alongside other interventions to support implementation and sustainability. 18 of the 22 studies reported sustained wait time and/or waitlist reductions at a minimum of 12-months postintervention, many with very large effect sizes. Two studies partially sustained reduced wait times and two studies were unable to achieve sustainability. No single type of intervention appeared to be more commonly associated with sustained reductions in wait time than others. Our review adds to the literature by demonstrating that implementing service-level interventions may lead to sustained reductions in wait times across diverse community and outpatient health services, despite well-described challenges in maintaining the outcomes of service improvement interventions. The interventions identified in these studies (referral entry, service access and substitution) shared common elements with previous reviews of wait time interventions but also had differences. Previous research considered referral entry and open access as a single intervention type, but they presented as two distinct categories in this group of studies. Substitution was classified in line with previous research but was only used in two studies as the primary intervention. Process efficiencies were not identified as a stand-alone intervention in this group of studies but were reported as being implemented alongside other primary interventions. The finding that no single category of intervention was superior in achieving sustained reductions in wait times is consistent with previous literature. Explicit use of additional resources was reported in eight of the studies, and it is possible that this addition of resources to a service (presumably increasing supply) is primarily responsible for the reduction in waiting times. While there was no clear pattern, all studies that specified additional resources did sustain reduced wait times, although there were also many examples of interventions that resulted in sustained wait time reductions without additional resources. Resources can be used to directly increase supply, but previous research has suggested that, in isolation, this approach is unlikely to result in sustained change. Consistent with this finding, none of the studies in this review reported using additional resources to temporarily increase supply within the existing model of care. Rather, any additional resources were used to support new models of care, such as adding an allied health practitioner or a patient navigator to the team. The additional resources were, therefore, not only used to supplement the supply available but also to disrupt the existing practices and act as an enabler to ongoing change. One factor that is likely to have contributed to the sustained changes reported in these studies is that all studies used strategies that were implemented as ongoing changes to the service. For example, changes to procedures and documentation for triaging referrals to clarify eligibility and identify appropriate services or appoint an allied health practitioner to reduce the load on more specialised health practitioners. Other studies used an analysis of supply and demand to inform the implementation of protected appointments for new patients or changes to the appointment types offered. All these interventions were implemented as new and ongoing processes that were not limited to a specific time period. Process efficiencies were frequently described and implemented alongside other interventions, often removing wasteful processes, consistent with ‘Lean’ methodology. These process changes may have supported change in behaviour that may have helped to achieve penetration of the intervention and sustained improvements. The quality of reporting for these studies was frequently low, contributing to a serious risk of bias and low certainty in the findings. The lack of clear descriptions of the interventions and reporting of fidelity in these studies results in difficulty for others to replicate the research process. These findings are aligned with research into the sustainability of service-level interventions in the literature, as well as findings from other reviews of waiting time interventions. With more comprehensive reporting, key components contributing to the sustainability of a service-level intervention would be better understood. We would then be better positioned to draw conclusions about what works and to confidently build on the previous research. Limitations of this review include the possibility of publication bias influencing the evidence in this field; however, this could not be formally assessed due to limitations of the available data. Only two studies reported on interventions that were not sustained at follow-up. Most studies in this review were framed as quality improvement activities or retrospectively described the impact of interventions that were intended to improve services, rather than being prospectively planned as research trials. This may increase the likelihood that those leading these types of innovations are more motivated to share a success story in which an intervention worked and achieved sustained change than those that have been unsuccessful. Defining sustainability as improvement maintained for 12-months post service-level intervention could be viewed as a limitation, as it may not consider the broader facets of sustainability, such as the extent to which changes are embedded in an organisation. However, this criterion enabled clear rules in relation to inclusion and exclusion. Additionally, the use of pragmatic thresholds for interventions to be considered sustained and/or have a large magnitude of effect could be considered a limitation, although the selection of conservative thresholds mitigates the likelihood of overinterpreting the findings as a result of this approach. 

This review suggests that reductions in wait times and waiting lists for health services may be achieved and often sustained following interventions at the health service level, but certainty of the evidence is low due to research designs with a high risk of bias and limitations in reporting. Further high-quality research would better inform service providers about what interventions are most effective and provide the greatest return on investment. Ongoing changes to the structure of referral and booking processes and/or changes to models of care that influence the flow of patients through healthcare systems appear to be a common feature in studies reporting sustained improvements in the delivery of timely care. 

10.1136/bmjoq-2024-003235 online supplemental file 1 10.1136/bmjoq-2024-003235 online supplemental file 2 

