Predicting fruit consumption: A multi-group application of the Theory of Planned Behavior

The main aim of the study was to test a two-wave longitudinal prediction model for the consumption of at least three portions of fruit per day, that was grounded on the Theory of Planned Behavior (TPB; Ajzen, 1991), extended with measures of past behavior and self-identity as a healthy eater. Self-identity is defined as a salient part of the self-concept specifically relates to a desirable behavior, such as, in this case, healthy eating. A second aim of the study was to test the invariance of the proposed model in two samples of Italian university students (n = 208) and no-student adults (n = 321). At time 1 the questionnaire was made up of measures of TPB constructs, with the addition of past consumption and self-identity as a healthy eater. Both the affective and evaluative components of attitude were assessed. At time 2, only the target behavior was surveyed. After checking both adequacy of the measurement model and reliability estimates, data were analyzed via structural equation modelling that returned good fit indices. Results showed that intention was positively associated with subjective norm, perceived behavioral control, self-identity and past behavior. Altogether, they explained 78% of the intention variance in the student group, and 81% in the adult group. After controlling for intention, past behavior - but not self-identity - was significantly related to the self-reported behavior, and the model explained 69% and 62% of behavior variance, respectively. Multi-sample analysis supported model invariance across the two groups. Results and their possible applications are presented and discussed.