***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Purpose The purpose of this study was to investigate the impact of low back pain ( LBP ) on future health-related quality of life ( HRQoL ) . Current evidence suggests that individuals with LBP have poorer HRQoL than those without LBP . However , most of the evidence comes from cross-sectional studies where LBP and HRQoL are determined at the same time . One prospect i ve study examined the association between days with LBP and HRQoL but did not account for the intensity of LBP . Therefore , this association needs to be tested in a large prospect i ve population -based sample with a valid measure of LBP and adequate control of known confounders . Methods We formed a cohort of 1,110 r and omly sample d Saskatchewan adults in September 1995 .  LBP at baseline was measured with the chronic pain question naire . The SF-36 question naire was used to measure physical and mental HRQoL at 6 months follow-up . Multivariable linear regression was used to estimate the association between grade d LBP at baseline and HRQoL at 6 months while controlling for the effects of confounding . Results The 6-month follow-up rate was 70.7 % ( 785/1,110 ) . LBP had a dose – response relationship with worsening physical HRQoL at 6 months , after controlling for age , income , arthritis , neck pain , and kidney disorders : grade III-IV LBP ( β = −10.23 ; 95 % CI −12.46 , −7.99 ) , grade II LBP ( β = −6.72 , 95 % CI −8.79 , −4.65 ) , and grade I LBP ( β = −1.77 ; 95 % CI −3.18 , −0.36 ) . There was no dose – response relationship between LBP and mental HRQoL at 6 months . Conclusions Low back pain has an impact on future physical HRQoL. Strategies for reducing the effects of LBP on HRQoL should be an important focus for clinicians , research ers , and health policy makers In a highly influential paper , Baron and Kenny ( 1986 ) proposed a statistical procedure to conduct a causal mediation analysis and identify possible causal mechanisms . This procedure has been widely used across many branches of the social and medical sciences and especially in psychology and epidemiology . However , one major limitation of this approach is that it is based on a set of linear regressions and can not be easily extended to more complex situations that are frequently encountered in applied research . In this paper , we propose an approach that generalizes the Baron-Kenny procedure . Our method can accommo date linear and nonlinear relationships , parametric and nonparametric models , continuous and discrete mediators , and various types of outcome variables . We also provide a formal statistical justification for the proposed generalization of the Baron-Kenny procedure by placing causal mediation analysis within the widely-accepted counterfactual framework of causal inference . Finally , we develop a set of sensitivity analyses that allow applied research ers to quantify the robustness of their empirical conclusions . Such sensitivity analysis is important because as we show the Baron-Kenny procedure and our generalization of it rest on a strong and untestable assumption even in r and omized experiments . We illustrate the proposed methods by applying them to a r and omized field experiment , the Job Search Intervention Study ( JOBS II ) . We also offer easy-to-use software that implements all of our proposed methods Most empirical tests of mediation utilize cross-sectional data despite the fact that mediation consists of causal processes that unfold over time . The authors considered the possibility that longitudinal mediation might occur under either of two different models of change : ( a ) an autoregressive model or ( b ) a r and om effects model . For both models , the authors demonstrated that cross-sectional approaches to mediation typically generate substantially biased estimates of longitudinal parameters even under the ideal conditions when mediation is complete . In longitudinal models where variable M completely mediates the effect of X on Y , cross-sectional estimates of the direct effect of X on Y , the indirect effect of X on Y through M , and the proportion of the total effect mediated by M are often highly misleading BACKGROUND Perceived social isolation is prevalent among patients with low back pain ( LBP ) and could be a potential prognostic factor for clinical outcomes following an episode of LBP . METHODS A secondary analysis of an original prospect i ve cohort study , which investigated the validity of the Danish version of the STarT Back Screening Tool ( STarT ) , investigated whether social isolation predicts the clinical outcomes of disability , anxiety , depression and pain catastrophizing in people with LBP . Patients with LBP of any duration ( N = 204 ) from Middelfart , Denmark , were included .  Social isolation  was measured at baseline using the friendship scale  ( score ranges from 0 to 24 , with lower values meaning higher perceived social isolation ) , and outcomes were measured at baseline and at 6-month follow-up . Regression models investigated whether social isolation at baseline predicted the outcomes at 6-month follow-up . RESULTS Some level of social isolation was reported by 39.2 % of the participants ( n = 80 ) with 5.9 % ( n = 12 ) being very socially isolated . One-point difference on social isolation predicted one point on a 100-point disability scale ( adjusted unst and ardized coefficient : -0.91 ; 95 % confidence interval ( CI ) : -1.56 to -0.26 ) . Social isolation predicted anxiety ; however , a change of one point on the social isolation scale represents a difference of only 0.08 points on a 22-point scale in anxiety ( 95 % CI : 0.01 - 0.15 ) and is unlikely to denote clinical importance . Social isolation did not predict pain catastrophizing or depression . CONCLUSIONS Patients ' perceived social isolation predicts disability related to LBP . Further underst and ing of the role of social isolation in LBP is warranted Purpose . The purpose of this study is to estimate the associations of psychosocial factors with pain and disability outcomes among neck-pain patients enrolled in a r and omized clinical trial of chiropractic treatments .  Methods . Neck-pain patients were r and omized to one of 8 modes of chiropractic treatment .  Health status and psychosocial variables were measured at baseline . Changes in neck pain severity and disability from baseline to 6 months were the primary outcome variables . Multivariable regression models were used to estimate effects of psychosocial variables adjusted for potential confounders . Results . Of 960 eligible patients , 336 were enrolled and 80 % were followed up through 6 months . Coping strategies involving self-assurance result ed in better disability outcomes , whereas getting angry or frustrated result ed in worse pain and disability outcomes . Participants with high levels of social support from individuals were more likely to experience clinical ly meaningful reductions in pain and disability . No consistent relations of internal health locus of control , and physical and psychological job dem and s with improvements in pain and disability were detected . Conclusions . We found some evidence that certain coping strategies and types of social support are associated with pain and disability outcomes in this population of largely subacute and chronic neck-pain patients & NA ; Although neck pain is a common source of disability , little is known about its incidence and course . We conducted a population ‐based cohort study of 1100 r and omly selected Saskatchewan adults to determine the annual incidence of neck pain and describe its course . Subjects were initially surveyed by mail in September 1995 and followed‐up 6 and 12 months later . The age and gender st and ardized annual incidence of neck pain is 14.6 % ( 95 % confidence interval : 11.3 , 17.9 ) . Each year , 0.6 % ( 95 % confidence interval : 0.0–1.1 ) of the population develops disabling neck pain . The annual rate of resolution of neck pain is 36.6 % ( 95 % confidence interval : 32.7 , 40.5 ) and another 32.7 % ( 95 % confidence interval : 25.5 , 39.9 ) report improvement . Among subjects with prevalent neck pain at baseline , 37.3 % ( 95 % confidence interval : 33.4 , 41.2 ) report persistent problems and 9.9 % ( 95 % confidence interval : 7.4 , 12.5 ) experience an aggravation during follow‐up . Finally , 22.8 % ( 95 % confidence interval : 16.4 , 29.3 ) of those with prevalent neck pain at baseline report a recurrent episode . Women are more likely than men to develop neck pain ( incidence rate ratio=1.67 , 95 % confidence interval 1.08–2.60 ) ; more likely to suffer from persistent neck problems ( incidence rate ratio=1.19 , 95 % confidence interval 1.03–1.38 ) and less likely to experience resolution ( incidence rate ratio=0.75 , 95 % confidence interval 0.63–0.88 ) . Neck pain is a disabling condition with a course marked by periods of remission and exacerbation . Contrary to prior belief , most individuals with neck pain do not experience complete resolution of their symptoms and disability & NA ; The mechanism or mechanisms involved in the development of pain‐related disability in people with low back pain is unclear . Psychological distress has been identified as one potential pathway by which an episode of pain influences the development of persistent disabling symptoms ; however , the relationship has not been formally investigated . This study investigated the causal relationship between pain and disability via psychological distress ( and its components depression , stress , and anxiety ) by using mediation path analysis . The study sample included 231 participants with subacute low back pain ( 6 to 12 weeks ’ pain duration ) who had been recruited for an exercise‐based r and omised , controlled trial . All participants  completed self‐report assessment s of pain ( 0–10 numerical rating scale ) , disability ( Rol and Morris Disability Question naire ) , and psychological distress ( Depression Anxiety and Stress Scale ) at baseline and again at 2 follow‐up time points ( 6 and 12 weeks after baseline ) . The results of the mediation analysis suggest that approximately 30 % of the relationship between subacute pain and later disability is dependent on the level of patients ’ psychological distress . The finding that psychological distress only partially ( 30 % ) mediated the pain‐disability relationship indicates that other factors should also be explored . Further analysis into the components of psychological distress revealed that the symptoms of depression and stress , but not anxiety , are responsible for mediation of the pain‐disability relationship . These findings provide an opportunity to decrease the risk of long‐term disability through early identification and management of depressive and stress symptoms . Psychological distress symptoms at 6 weeks in patients with low back pain  influences future disability . Symptoms of depression and stress , but not anxiety , are responsible for mediation of the pain‐disability & NA ; The association of self‐efficacy expectancies with pain tolerance on the cold pressor test was examined during treatment conditions of setting quotas alone and in conjunction with monetary reinforcement and placebos in 64 college volunteers . It was found that quota setting was an effective means of increasing cold presser pain tolerance . The addition of monetary reinforcement of quota achievement did not enhance performance , while the addition of a placebo decreased the effectiveness of quota setting . Self‐efficacy expectancies were significantly correlated with pain tolerance times and were better predictors of tolerance than pain ratings . Self‐efficacy expectancies and pain tolerance times at treatment were both found to predict 1 week follow‐up performance 
    Output:
    
Nonetheless , the results suggest that there are significant mediating effects of self-efficacy , psychological distress , and fear , which underpins the direct targeting of these constructs in treatment