Social influence in the theory of planned behaviour: the role of descriptive, injunctive, and in-group norms.

The present research investigated three approaches to the role of norms in the theory of planned behaviour (TPB). Two studies examined the proposed predictors of intentions to engage in household recycling (Studies 1 and 2) and reported recycling behaviour (Study 1). Study 1 tested the impact of descriptive and injunctive norms (personal and social) and the moderating role of self-monitoring on norm-intention relations. Study 2 examined the role of group norms and group identification and the moderating role of collective self on norm-intention relations. Both studies demonstrated support for the TPB and the inclusion of additional normative variables: attitudes; perceived behavioural control; descriptive; and personal injunctive norms (but not social injunctive norm) emerged as significant independent predictors of intentions. There was no evidence that the impact of norms on intentions varied as a function of the dispositional variables of self-monitoring (Study 1) or the collective self (Study 2). There was support, however, for the social identity approach to attitude-behaviour relations in that group norms predicted recycling intentions, particularly for individuals who identified strongly with the group. The results of these two studies highlight the critical role of social influence processes within the TPB and the attitude-behaviour context.