Heterogeneous treatment effects of a text messaging smoking cessation intervention among university students

Introduction: Despite tobacco being an important preventable factor with respect to ill health and death, it is a legal substance that harms and kills many of those who use it. Text messaging smoking cessation interventions have been evaluated in a variety of contexts, and are generally considered to have a positive effect on smoking cessation success. In order for text messaging interventions to continue to be useful as prevalence of smoking decreases, it may be necessary to tailor the interventions to specific individuals. However, little is known with regard to who benefits the most and least from existing interventions. Methods: In order to identify heterogenous treatment effects, we analyzed data from a randomized controlled trial of a text messaging smoking cessation intervention targeting university students in Sweden. We used a Bayesian hierarchical model where the outcome was modelled using logistic regression, and so-called horseshoe priors were used for coefficients. Predictive performance of the model, and heterogeneous treatment effects, were calculated using cross-validation over the trial data. Results: Findings from the study of heterogenous treatment effects identified less effect of the intervention among university students with stronger dependence of nicotine and students who smoke a greater quantity of cigarettes per week. No heterogeneity was found with respect to sex, number of years smoking, or the use of snuff. Discussion: Results emphasize that individuals with a more developed dependence of nicotine may have a harder time quitting smoking even with support. This questions the dissemination and development of text messaging interventions to university students in the future, as they may not be the optimal choice of intervention for those with a more developed dependence. On the other hand, text messaging interventions may be useful to disseminate among university students that are at risk of developing a strong dependence. Trial registration: International Standard Randomized Controlled Trial Number (ISRCTN): 75766527; http://www.controlled-trials.com/ISRCTN75766527.