The effect of forming implementation intentions on alcohol consumption: A systematic review and meta-analysis
Issues: Meta-analysis was used to estimate the effect of forming implementation intentions (i.e., if-then plans) on weekly alcohol consumption and heavy episodic drinking (HED). Sample type, mode of delivery, intervention format and timeframe were tested as moderator variables. Approach: Cochrane, EThOS, Google Scholar, PsychArticles, PubMed and Web of Science were searched for relevant publications to 31 March 2021. Random-effects meta-analysis was used to estimate the effect size difference (d) between individuals forming versus not forming implementation intentions on weekly consumption and HED. Key Findings: Sixteen studies were included in meta-analyses. The effect size difference for forming implementation intentions on weekly alcohol consumption was d+ = −0.14 confidence interval (CI) [−0.24; −0.03]. Moderator analyses highlighted stronger effects for: (i) community (d+ = −0.38, CI [−0.58; −0.18]) versus university (d+ = −0.04, CI [−0.13; 0.05]) samples; (ii) paper (d+ = −0.26, CI [−0.43; −0.09]) versus online (d+ = −0.04, CI [−0.14; 0.06]) mode of delivery; and (iii) volitional help sheet (d+ = −0.34, CI [−0.60; −0.07]) versus implementation intention format (d+ = −0.07, CI [−0.16; 0.02]). In addition, effects diminished over time (B = 0.02, SE = 0.01, CI [0.03; 0.01]). Forming implementation intentions had a null effect on HED, d+ = −0.01 CI [−0.10; 0.08]. Implications: Forming implementation intentions reduces weekly consumption but has no effect on HED. Conclusion: This review identifies boundary conditions on the effectiveness of implementation intentions to reduce alcohol consumption. Future research should focus on increasing the effectiveness of online-delivered interventions and integrating implementation intention and motivational interventions.