title: Small-scale randomized controlled trials need more powerful methods of mediational analysis than the Baron-Kenny method.
abstract: OBJECTIVE
  To devise more-effective physical activity interventions, the mediating mechanisms yielding behavioral change need to be identified. The Baron-Kenny method is most commonly used, but has low statistical power and may not identify mechanisms of behavioral change in small-to-medium size studies. More powerful statistical tests are available.
  
  
  METHODS
  Inactive adults (N=52) were randomized to either a print or a print-plus-telephone intervention. Walking and exercise-related social support were assessed at baseline, after the intervention, and 4 weeks later. The Baron-Kenny and three alternative methods of mediational analysis (Freedman-Schatzkin; MacKinnon et al.; bootstrap method) were used to examine the effects of social support on initial behavior change and maintenance.
  
  
  RESULTS
  A significant mediational effect of social support on initial behavior change was indicated by the MacKinnon et al., bootstrap, and, marginally, Freedman-Schatzkin methods, but not by the Baron-Kenny method. No significant mediational effect of social support on maintenance of walking was found.
  
  
  CONCLUSIONS
  Methodologically rigorous intervention studies to identify mediators of change in physical activity are costly and labor intensive, and may not be feasible with large samples. The use of statistically powerful tests of mediational effects in small-scale studies can inform the development of more effective interventions.
authors.affiliation: Cancer Prevention Research Centre, School of Population Health, The University of Queensland, Herston Road, Herston, Brisbane, QLD 4006, Australia. ecerin@hku.hk
authors.forename: Ester
authors.initials: E
authors.lastname: Cerin
authors.forename: Lorian M
authors.initials: LM
authors.lastname: Taylor
authors.forename: Eva
authors.initials: E
authors.lastname: Leslie
authors.forename: Neville
authors.initials: N
authors.lastname: Owen
mesh_terms: D000368:Aged; D015444:Exercise; D005260:Female; D015438:Health Behavior; D006266:Health Education; D006293:Health Promotion; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D012944:Social Support; D013689:Telephone; D016138:Walking