title: Use of the varying coefficient model in an exercise and depression meta-analysis.
abstract: OBJECTIVE
  Use a recently developed varying coefficient model to determine the effects of exercise in adults with depression.
  
  
  METHODS
  Data from a recent meta-analysis addressing the effects of exercise on depression in adults were used. Studies were limited to randomized controlled intervention trials of any type of chronic exercise (for example, walking and jogging) in adults greater than or equal to 18 years of age with a diagnosis of depression. For each study, the standardized mean difference (exercise minus control) effect size for depression, adjusted for small-sample bias, was calculated. Variance statistics for each effect size and pooling of results were calculated using the recently proposed varying coefficient (VC) model for standardized mean differences. Standardized effect-sizes of 0.20, 0.50 and 0.80 were considered to represent small, medium and large effects. Results were considered statistically significant if the 95% confidence intervals did not cross 0, with negative results indicative of reductions in depression. These findings were then compared with results using traditional random-effects (RE) models.
  
  
  RESULTS
  A total of 23 studies representing 907 men and women (476 exercise, 431 control) were pooled for analysis. Both RE and VC models resulted in large, statistically significant improvements in depression as a result of exercise in adults. However, the VC model resulted in a larger overall effect size as well as confidence intervals that were narrower than previously reported using the RE model. The overall mean effect size for the RE model was -0.82 with a 95% confidence interval of -1.12 to -0.51. For the VC model, overall mean effect size was -0.88 with a 95% confidence interval of -1.08 to -0.68. The relative difference between the RE and VC approaches was 7.3%.
  
  
  CONCLUSIONS
  The VC model, a potentially preferable model, confirms the positive effects of exercise on depression in adults.
authors.affiliation: George A Kelley, Kristi S Kelley, Meta-Analytic Research Group, Department of Community Medicine, School of Medicine, Robert C Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26506, United States.
authors.forename: George A
authors.initials: GA
authors.lastname: Kelley
authors.affiliation: George A Kelley, Kristi S Kelley, Meta-Analytic Research Group, Department of Community Medicine, School of Medicine, Robert C Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26506, United States.
authors.forename: Kristi S
authors.initials: KS
authors.lastname: Kelley
keywords: Depression; Exercise; Meta-analysis; Random-effects; Varying coefficient