First- and higher-order models of attitudes, normative influence, and perceived behavioural control in the theory of planned behaviour.

The present study examined the validity of an augmented version of Ajzen's (1991) theory of planned behaviour (TPB), adopting second-order latent factors to explain relationships between the differentiated components of the theory constructs. This model was tested on data from two independent samples, for exercise and dieting behaviours, respectively. The affective and instrumental attitude, injunctive and descriptive norms, and perceived controllability and self-efficacy constructs all exhibited discriminant validity in the first instance. First- and second-order confirmatory factor analyses exhibited satisfactory fit with the observed data from both samples. There were no substantial differences in the fit indices across the first- and second-order models, and the second-order models exhibited the most optimal parsimony-corrected fit indices. The higher-order models could therefore not be rejected on the grounds of inferior fit or parsimony. First- and second-order structural equation models accounted for significant variance in intentions and behaviour. These results corroborate Ajzen's (2002a) and Bagozzi, Lee, and van Loo's (2001) premise that recent augmentations of the TPB that differentiate the model components can be subsumed by global, higher-order factors while still making the distinction at the subordinate level.