Abstract
Adolescents intention to drink alcohol with peers was measured using an extended version of the Theory of Planned Behaviour (TPB) on a sample consisting of 617 10th graders in Oslo, Norway. The aim was to investigate the influence of social factors from a theoretical and an applied perspective. In particular, different ways of operationalising subjective norms were investigated, as were the presumed effect of descriptive norms and group identity as additional variables in the TPB. Considering the young population and the nature of the behaviour investigated, it was assumed that, within this extended TPB model, social factors would show stronger effects than previously reported in TPB studies. Overall, the extended TPB model fared well and explained 63.8 % of the variance in intention to drink alcohol with peers. Support was found for the indirect measure of subjective norms based on normative beliefs without motivation to comply. Furthermore, significant results were obtained for the inclusion of descriptive norms, group identity as a moderator of descriptive norms and, surprisingly, main effect of group identity. Contrary to expectations, however, social factors did only show marginal effects on intention to drink, whereas attitude was found to be the strongest predictor of intention. The results are discussed in relation to development of the TPB and consequences for alcohol prevention programs. In particular, a seemingly increased importance of personal factors on adolescent risk-behaviour in the late modernity is discussed.