An Intervention to Reduce Alcohol Consumption in Undergraduate Students Using Implementation Intentions and Mental Simulations: A Cross-National Study

Previous intervention studies have shown that the significant effects of implementation intention and planning manipulations on alcohol consumption are confined to female samples [41]. This differential effectiveness was a concern in the present study given the variation in gender profiles across the three national samples. One possibility was that the higher proportion of female participants in the UK sample and, to a lesser extent, the Estonian sample, may have accounted for the significant findings for the implementation intention manipulation on the alcohol behavior variables in these samples, relative to the Finnish sample which had the closest ratio of males to females and showed no effects. As a consequence, we conducted supplementary ANCOVAs with gender as an additional independent factor to test the hypothesis that gender moderated the effect of the interventions. Specifically, we conducted two 2 (implementation intention: present vs. absent) × 2 (mental simulation: present vs. absent) × 3 (nationality: Estonia vs. Finland vs. UK) × 2 (gender: male vs. female) ANCOVAs on the dependent variables of average number of units of alcohol and number of binge-drinking occasions in the month following the intervention. The analyses revealed an identical pattern of effects as the main analyses. Specifically, the analysis with number of units consumed as the dependent variable revealed significant main effects for implementation intentions (F(1, 440) = 6.36, p < 0.05, η _p ²  = 0.01) and nationality (F(2, 440) = 5.42, p < 0.01, η _p ²  = 0.02), and a significant implementation intention × nationality interaction (F(2, 440) = 5.73, p < 0.01, η _p ²  = 0.03). The analysis with number of binge-drinking occasions as the dependent variable revealed a significant main effect for nationality (F(1, 440) = 3.60, p < 0.05, η _p ²  = 0.02) and a significant implementation intention × nationality interaction effect (F(2, 440) = 4.26, p < 0.05, η _p ²  = 0.02). In both analyses, there was no significant main effect for gender or any effect of the two-, three-, or four-way interactions between gender and the other independent variables on alcohol behavior. These data led us to reject the hypothesis that gender moderated the effects of the intervention components, specifically, implementation intentions, on alcohol behavior.

We also tested whether the inclusion of participants who consumed no alcohol at baseline affected results. Specifically, we conducted analyses on participants reporting drinking at least 1 U of alcohol in the previous 4 weeks at baseline. We conducted two additional 2 (implementation intention: present vs. absent) × 2 (mental simulation: present vs. absent) × 3 (nationality: Estonia vs. Finland vs. UK) ANCOVAs with number of units of alcohol consumed and number of binge-drinking occasions as dependent variables and controlling for baseline FAST scores, alcohol consumption, and attitudes. For the analysis with number of units consumed as the dependent variable, the analysis revealed significant main effects for implementation intention (F(1, 399) = 3.72, p < 0.05, η _p ²  = 0.01) and nationality (F(2, 399) = 8.21, p < 0.01, η _p ²  = 0.04), and a significant two-way interaction for implementation intentions and nationality (F(2, 399) = 3.19, p < 0.05, η _p ²  = 0.02). This interaction was probed with separate univariate ANCOVAs for each national group. The analyses revealed significant main effects for implementation intentions in the Estonia (F(1, 155) = 4.41, p < 0.05, η _p ²  = 0.03), and UK (F(1, 158) = 10.58, p < 0.01, η _p ²  = 0.07) samples. For the analysis with number of binge-drinking occasions as the dependent variable, a significant main effect for nationality (F(1, 399) = 6.01, p < 0.01, η _p ²  = 0.03) and a significant two-way interaction for implementation intentions and nationality (F(2, 399) = 4.27, p < 0.05, η _p ²  = 0.02) was found. Separate univariate ANCOVAs revealed a similar main effect for implementation intentions as that found previously for the UK sample (F(1, 158) = 6.50, p < 0.05, η _p ²  = 0.04). There were no other significant effects. These results, therefore, follow a similar pattern to those found in the overall sample.

Mean levels of intentions were significantly higher than the midpoint of the six-point scale for the Estonian (M = 4.74, SD = 1.19; t(1,184) = 14.19, p < 0.01, d = 2.09), Finnish (M = 4.03, SD = 1.73; t(1,118) = 3.37, p < 0.01, d = 0.62), and UK samples (M = 3.96, SD = 1.33; t(1,162) = 4.42, p < 0.01, d = 0.69).