Test of a brief theory of planned behaviour-based intervention to promote adolescent safe sex intentions

The present study tested a brief ( 303 word) intervention designed to change attitude, subjective norm, and perceived behavioural control regarding a safe sex behaviour in a sample of 16- to 18-year-olds. Participants (N = 288) were randomized to receive either an experimental intervention or a control ( knowledge only) intervention and completed measures of their reactions to the stimuli as well as pre- and post-test measures of theory of planned behaviour variables. The experimental intervention significantly increased message processing ( mean between-group difference = 0.73, 95% CI = 0: 40, 1.06; Cohen's d = .52), message acceptance ( mean between-group difference = 0.82, 95% CI = 0.57, 1.07; Cohen's d = .77), subjective norm ( adjusted Mean between-group difference = 0.54, 95% CI = 0.26, 0.81; Cohen's d = .37; mean within-group difference for intervention condition = 0.59, 95% CI = 0.36, 0.81; Cohen's d = .38) and intention ( adjusted Mean between-group difference = 0.27, 95% CI = 0.02, 0.53; Cohen's d = .20; mean within-group difference for intervention condition = 0.54, 95% CI = 0.33, 0.75; Cohen's d = .31), but not attitude or perceived behavioural control. The effects of the experimental intervention on intention were mediated solely through subjective norm. The present findings: ( a) compare favourably in terms of the effect sizes reported in previous research in this area ( mean Cohen's d for within-group difference for intervention conditions = .009 and .09, for norms and intention, respectively, see Albarracin et al. ( 2003)), (b) imply that subjective norms are causally related to intentions, and ( c) suggest that interventions designed to change subjective norms ( as opposed to communication of risks and fear appeals) might ultimately be effective in changing behaviour.