Eating three portions of fruit per day. A two-wave TPB-based multi-group study

The main aim of the study was to test a prediction model grounded on the Theory of Planned Behaviour (TPB; Ajzen, 1991), extended with self-identity as a healthy eater and past behaviour. Self-identity is a salient part of the self-concept specifically relates to a desirable behaviour, such as, in this case, healthy eating. The target behaviour was the consumption of at least three portions of fruit per day. A second aim of the study was to test the invariance of the model in Italian university students and no-student adults. The research involved 208 university students and 321 no-students and was based on two waves of data collection. At time 1 the questionnaire was made up of measures of all classical TPB constructs, plus measures of past consumption and of self-identity as a healthy eater. Both the affective and evaluative components of attitude were assessed. At time 2, only the target behaviour was surveyed. Data were analysed by means of structural equation modeling that returned good fit indices in any case. Results showed that intention was positively associated with subjective norm, perceived behavioural control, self-identity and past behaviour. Altogether, they explained 78% of the intention variance in the student group, and 81% in the adult group. After controlling for intention, past behaviour – but not self-identity – was significantly related to the self-reported behaviour. The model explained 69% of behaviour variance for students and 62% for no-students. The chi-square difference tests supported model invariance across the two groups.