Self-identity and the theory of planned behaviour: between- and within-participants analyses.

Two studies addressed the hypothesis that a minority of people are more oriented towards their self-identity when forming intentions to act than the traditional antecedents of intentional action; attitudes, subjective norms and perceived behavioural control (PBC). In Study 1, participants (N=241) completed measures of an augmented version of theory of planned behaviour (TPB) that included self-identity for 30 behaviours. Using within-participants multiple regression analyses, the sample was classified into self-identity-oriented (SI-oriented) and TPB-oriented groups. Between-participants multiple regression analyses revealed that self-identity was a significantly stronger predictor of intentions and accounted for significantly more incremental variance in intentions in the SI-oriented sample compared with the TPB-oriented sample across the 30 behaviours. In Study 2, participants (N=250) completed the same TPB and self-identity measures used in Study 1 as well as measures of generalized self-concept and social physique anxiety for dieting behaviour. Results indicated that self-identity was significantly associated with the generalized self-related measures, and self-concept and social physique anxiety moderated the self-identity-intention relationship. This investigation provides some preliminary evidence to support the effect of individual differences in self-identity on the formation of intentions to act.