Prospective prediction of health-related behaviours with the Theory of Planned Behaviour: a meta-analysis

This meta-analysis explored the efficacy of the Theory of Planned Behaviour (TPB) dependent on behaviour and methodological moderators. A lack of hierarchical analysis in previous reviews risks confounding these moderators. Here moderating roles of behaviour type, length of follow-up, sample age and behavioural measure are explored hierarchically amongst prospective tests of the TPB, controlling for past behaviour where possible. Searching identified 237 prospective tests from 206 articles. Random-effects meta-analytic procedures were used to correcting correlations for sampling and measurement error. Behaviour type moderated the model; physical activity and diet behaviours were better predicted (23.9% and 21.2% variance explained, respectively) whilst risk, detection, safer sex and abstinence from drugs were poorly predicted (between 13.8 and 15.3% variance explained). Methodological moderators were also apparent: age of sample moderated relations with student samples better predicted for physical activity, and adolescent samples better predicted for abstinence behaviours. Behaviours assessed in the shorter term, and those assessed with self-reports (compared with objective measures) were also better predicted. Both behavioural and methodological characteristics moderated relations amongst model components. The results can aid selection of appropriate targets upon which to base interventions.