JMIR Publications

ABSTRACT

Background:

Background:

Many digital interventions for unhealthy alcohol use are based on personalized normative feedback (PNF) and personalized feedback on risks for health (PFR). The hypothesis is that PNF and PFR affect drinkers’ perceptions of drinking norms and risks, respectively, resulting in changes in drinking behaviors. Moreover, since PNF is thought to correct overestimations of other people’s drinking, it should primarily affect the perceptions of drinking norms of individuals who overestimate other people’s drinking.

Objective:

Objectives: To investigate whether these mechanisms mediated the effects of a smartphone-based intervention to reduce alcohol use.

Methods:

Methods:

1,770 students from four higher education institutions in Switzerland (mean [SD] age = 22.35 years [3.07]) who had screened positive for unhealthy alcohol use were randomized to receive access to a smartphone application or to the no-intervention control condition. The smartphone application provided PNF and PFR. Outcomes were drinking volume (DV) in standard drinks per week and the number of heavy drinking days (HDDs) assessed at baseline and 6 months. Mediators were perceived drinking norms and perceived risks for health measured at baseline and 3 months. Parallel mediation analyses and moderated mediation analyses were conducted to test whether: 1) the intervention effect was indirectly related to lower DV and HDDs at 6 months (adjusting for baseline values) through perceived drinking norms and perceived risks for health at 3 months (adjusting for baseline values); 2) the indirect effects through perceived drinking norms differed between participants who overestimated or who did not overestimate other people’s drinking at baseline.

Results:

Results:

The intervention’s total effects were significant (DV: b = -0.85[95% bootstrap confidence interval -1.49; -0.25]; HDD: b = -0.44[-0.72; -0.16]), indicating less drinking at 6 months in the intervention group than in the control group. The direct effects (i.e., controlling for mediators) were significant though smaller (DV: b = -0.73[-1.33; -0.16]; HDD: -0.39[-0.66; -0.12]). For DV, the indirect effect was significant through perceived drinking norms (b = -0.12[-0.25; -0.03]). The intervention was associated with lower perceived drinking norms at 3 months (b = -0.80[-1.36; -0.22]), and perceived drinking norms at 3 months were associated with DV at 6 months (b = 0.15[0.08; 0.24]). The indirect effects through perceived risk (for DV and HDD) and through perceived drinking norms (for HDD) were not significant. Results of moderated mediation analyses showed that the indirect effects through perceived drinking norms were significant among participants overestimating other people’s drinking (DV: b = -0.17[-0.32; -0.05]; HDD: -0.08[-0.15; -0.01]) but not significant among those not overestimating.

Conclusions:

Conclusions:

Perceived drinking norms, but not perceived risks, partially mediated the intervention’s effect on alcohol use, confirming one of its hypothesized mechanisms of action. These findings lend support to using normative feedback interventions to discourage unhealthy alcohol use. Clinical Trial: Trial registration ISRCTN 10007691; https://doi.org/10.1186/ISRCTN10007691