Examining trends, predictors, and mediators of e-cigarette use and smoking among Canadian youth: Findings from the COMPASS study

Abstract The objectives of this dissertation were to (1) examine trends and predictors of youth e-cigarette use and cigarette smoking, (2) explore potential mediators of the association between initial e-cigarette use and cigarette smoking uptake, and (3) evaluate the impact of Ontario’s introduction of e-cigarette minimum legal sales age (MLSA) laws on youth e-cigarette use. The study objectives were explored in three separate manuscripts using data gathered from a sample of students in two Canadian provinces, Ontario and Alberta, that participated in a school-based study (COMPASS). Using longitudinal data from students in Ontario and Alberta, the first manuscript examined changes in the prevalence of exclusive e-cigarette use, exclusive smoking and dual use of e-cigarettes and cigarettes over time. This manuscript also examined how frequency of e-cigarette use and smoking (i.e., number of days used in the past month) predicted exclusive e-cigarette use, exclusive cigarette smoking and dual use of both products after a one- and two-year follow-up period. Study findings showed an increase in all usage categories over time. Findings also demonstrated some differences in predictors of exclusive e-cigarette use, exclusive smoking and dual use. For instance, frequent e-cigarette use (i.e., use for 4 or more days in past month) was not a significant predictor of exclusive smoking at either follow-up time point, but did predict dual use at both the one- and two-year follow-up. Notably, findings also showed that students who reduced their frequency of e-cigarette use were less likely to report being exclusive e-cigarette users and dual users at the two-year follow-up. The second manuscript investigated whether having one or more smoking friends mediated the association between initial e-cigarette use and cigarette smoking onset among a longitudinal sample of youth who were never smokers at baseline. Longitudinal findings showed that having one or more smoking friends did not mediate the association between e-cigarette use and subsequent cigarette smoking. Similarly, longitudinal results showed that having smoking friends did not mediate the association between e-cigarette use and subsequent dual use of e-cigarettes and cigarettes. Rather, our study findings indicated that smoking friends significantly predicted both e-cigarette use and cigarette smoking among youth. The third manuscript evaluated the influence of an e-cigarette law introduced in Ontario using a quasi-experimental design. In January 2016, Ontario implemented a law restricting the sale of e-cigarettes to those 19 and over. At that time, Alberta did not have a similar law in effect. Using a repeat cross-sectional sample, we examined the impact of Ontario’s law on the school-level prevalence of e-cigarette use among a sample of Ontario schools versus Alberta schools. Furthermore, using a longitudinal sample of students, we evaluated the impact of this law on the individual likelihood of e-cigarette use among students in Ontario versus Alberta schools. Findings based on the repeat cross-sectional sample showed that the changes in the average school-level prevalence of e-cigarette use within the Ontario sample were not significantly different from the changes seen in the Alberta sample. Findings based on the longitudinal sample showed increases in e-cigarette use over time among students in Ontario and Alberta. However, the increase observed among students in Alberta (i.e., where no e-cigarette MLSA law was implemented) was larger than the increase seen among students in Ontario (i.e., where an e-cigarette MLSA law was implemented). The studies examined within this dissertation project contribute towards our understanding of e-cigarette use and cigarette smoking among Canadian youth. Longitudinal findings indicated that having one of more smoking friends is a common risk factor that is associated with both e-cigarette use and cigarette smoking among youth. These findings suggest that the role of peers should be considered within the design of youth-based prevention interventions. Longitudinal findings showed an increase in e-cigarette use over time among youth in our study sample. Longitudinal findings also indicated that Ontario’s introduction of e-cigarette MLSA laws had an impact in attenuating these increases in e-cigarette use, but did not reverse the overall increasing trend in use among youth in our sample. Collectively, our study findings suggest the need for a more comprehensive approach to address the rise in e-cigarette use among Canadian youth