Descriptive norms as an additional predictor in the theory of planned behaviour: A meta-analysis

This study used meta-analysis: (a) to quantify the relationship between descriptive norms and intentions, and (b) to determine the increment in variance attributable to descriptive norms after variables from the theory of planned behaviour (TPB; Ajzen, 1991) had been controlled. Literature searches revealed twenty-one hypotheses based on a total sample of N = 8097 that could be included in the review. Overall, there was a medium to strong sample-weighted average correlation between descriptive norms and intentions (r(+) =.44). Regression analysis showed that descriptive norms increased the variance explained in intention by 5 percent after attitude, subjective norm, and perceived behavioural control had been taken into account. Moderator analyses indicated that younger samples and health risk behaviours were both associated with stronger correlations between descriptive norms and intentions. Implications of the findings for the conceptualization of social influences in the TPB are discussed.