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Integrating the theory of planned behaviour and self-determination theory in health behaviour: a meta-analysis.

PURPOSE
A meta-analysis of studies integrating the theory of planned behaviour (TPB) and self-determination theory (SDT) in health contexts is presented. The analysis aimed to provide cumulative empirical support for a motivational sequence in which self-determined motivation from SDT predicts the proximal predictors of intentions and behaviour from the TPB.


METHODS
A literature search identified 36 integrated studies providing 45 tests of effects between TPB and SDT variables. Hunter and Schmidt's (1994) methods of meta-analysis were used to correct the effect sizes across the studies for statistical artifacts. Age (old versus young), publication status (published versus unpublished), study design (correlational versus experimental/intervention), and behaviour type (physical activity versus other health-related behaviours) were evaluated as moderators of the effects. A path-analysis using the meta-analytically derived correlations was conducted to examine the proposed motivational sequence.


RESULTS
Statistically significant corrected correlations were evident among the perceived autonomy support and self-determined motivation constructs from SDT and the attitude, subjective norms, perceived behavioural control, intention, and health-related behaviour constructs from the TPB. Only six of the 28 effect sizes were moderated by the proposed moderators. Path analysis revealed that the significant effects of self-determined motivation on intentions and behaviour were partially mediated by the proximal predictors from the TPB.


CONCLUSIONS
Evidence from this synthesis supported the theoretical integration and proposed motivational sequence. Results are discussed with reference to the complementary aspects of the TPB and SDT and the need for integrated experimental or intervention studies on a broader range of health behaviours.