No abstract

Objectives. This study examined the application of the Theory of Planned Behaviour (TPB) to two dietary behaviours with a particular focus on the roles of perceived control and self-ef cacy as two components of the perceived behaviouralcontrol construct in the TPB. Methods.A total of 287 members of the general public completed questionnaires, one concerning the in uence of TPB variables on intentions and behaviour for either eating ve portions of fruit and vegetables per day (N 5 144) or eating a low-fat diet (N 5 143), and the second concerning actual eating behaviour one month later. In addition, the individual components of perceived behavioural control (perceived control and self-ef cacy) and their determinant beliefs were examined. Results.For each behaviour, the TPB variables were found to be good predictors of intentions (fat intake, R 2 5 .637; fruit and vegetable intake, R 2 5 .572), although less good at predicting behaviour (fat intake, R 2 5 .185; fruit and vegetable intake, R 2 5 .321), with self-ef cacy being consistently more predictive than perceived control. In addition, examination of their determinant beliefs revealed self-ef cacy and perceived control to have difference bases. The conceptual and empirical distinctions between perceived control and self-ef cacy are discussed.

This paper examines the additive and moderating effects of social influence variables (injunctive norms, descriptive norms, perceived social support) within the Theory of Planned Behaviour (TPB). The target behaviour is the decision to eat healthily. Questionnaire responses on components of the TPB, descriptive norms, perceived social support, and subsequent healthy eating were obtained from a prospective sample of 235 members of the general public. Good predictions of intentions (42% of variance explained) and behaviour (15% of variance explained) were found using the Theory of Planned Behaviour. Neither descriptive norms nor perceived social support added to these predictions of intentions over and above the TPB variables. However, perceived social support was found to act as a moderator variable on the relationship between perceived behavioral control and intention, and the relationship between attitude and intention. Implications for exploring the role of social influence variables on decisions concerning health behavioun an discussed.

The research supports the widespread view that ambivalence is an important issue, both for those involved in basic attitude research and for those who seek to use attitude theories in applied research. In particular, the findings indicate that ambivalence may often have implications for the predictive ability of attitude-intention-behaviour models, especially when applied to health-related behaviours that are characterized by motivational conflicts.

The present study examined the moderating role of attitudinal ambivalence within the theory of planned behaviour (TPB). Attitude, subjective norm, perceived behavioural control (PBC), behavioural intentions and self-reported behaviour were assessed in relation to 20 healthy eating behaviours in a prospective questionnaire design in 232 members of the general public in the UK. Between-participants univariate and multivariate analyses indicated attitude-behaviour and PBC-behaviour relationships to be weaker in higher ambivalence compared to lower ambivalence respondents. These effects were confirmed in within-participants analyses. The findings are discussed in terms of the role of ambivalence in furthering our understanding of relationships in the TPB.