Interaction effects in the theory of planned behaviour: Studying cannabis use

Abstract

This study employed the theory of planned behaviour (TPB) to investigate the factors underlying intentions and frequency of use of cannabis over a three‐month period in a population of students (N=249). In addition, several hypotheses in relation to the TPB were investigated. The TPB provided good predictions of both intentions (R2=0.653; attitude, injunctive norms and perceived behavioural control significant) and behaviour (R 2 =0.711; intentions significant). Other norm measures (descriptive and moral norms) explained additional variance in intentions. ( p <.01). In addition, habit strength and self‐identity explained significant additional portions of the variance in intentions ( p <.001), but not behaviour, over and above the TPB variables. Several interactions among these variables were also tested. Attitude moderated the impact of perceived behavioural control (PBC) on intentions ( p <.001). Moral norms moderated the impact of attitudes on intentions ( p <.001). Habit strength moderated the impact of self‐identity on intentions ( p <.001). PBC was found to moderate the impact of intentions on behaviour ( p <.05). The findings are discussed in relation to how interaction effects further our understanding of the social processes by which variables are related in the TPB.

Keywords

Affiliated Institutions

• University of Leeds GB

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