Predictive validity of the theory of planned behaviour: The role of questionnaire format and social desirability

The present study was designed to assess the predictive validity of a theor y of planned behaviour extended to include self-identity, in the context of health-related food choice. Following criticism of the use of questionnair es in social cognitive research, the impact of questionnaire format (random vs structured) and social desirability on questionnaire responses was asse ssed. Findings indicated that intention was the principal determinant of fo od choice; attitude, subjective norm and self-identity were independently p redictive of intention. There was only weak evidence to suggest effects of social desirability or questionnaire format on component relationships. The present study indicates that the impact of questionnaire format and social desirability on models such as the theory of planned behaviour is minimal, and that such models are robust predictors of food choice. Copyright (C) 1 999 John Wiley & Sons, Ltd.