Does theory influence the effectiveness of health behavior interventions? Meta-analysis.

To systematically investigate the extent and type of theory use in physical activity and dietary interventions, as well as associations between extent and type of theory use with intervention effectiveness.

An in-depth analysis of studies included in two systematic reviews of physical activity and healthy eating interventions (k = 190). Extent and type of theory use was assessed using the Theory Coding Scheme (TCS) and intervention effectiveness was calculated using Hedges's g. Metaregressions assessed the relationships between these measures.