A multicomponent model of the theory of planned behaviour.

The purpose of this study was to investigate the measurement and predictive structure of multiple components of attitude (affective and instrumental), subjective norm (injunctive and descriptive) and an alternative measure of perceived behavioural control (PBC; skills/ability, opportunity, and resources) in the exercise domain. An additional purpose of the study was to compare the validity of the alternative PBC measure to a standard PBC measure for predicting exercise intention and behaviour. Participants were 220 undergraduates who completed measures of the theory of planned behaviour (TPB) and a 2-week follow-up of exercise behaviour. Results supported the discriminant validity in the measurement domains of all TPB components. Predictive validity of exercise behaviour for these components, however, was only evident for attitude and PBC components. Our alternative PBC measure was found commensurate with the standard PBC measure. Finally, intention significantly (p < .05) predicted exercise behaviour (R2 = .42), while affective attitude, and perceived opportunity significantly (p < .05) predicted intention (R2 = .47).