Discussion
PMT
The results of the present study support the view that both threat appraisals (PV and PS) grounded in PMT are effective mechanisms to reduce vaping intentions among a sample of Canadian university students who regularly vape. With respect to vaping use, we found inconsistent and thus less convincing evidence for the effectiveness of the PMT intervention. Beyond these general findings, a number of specific issues warrant further commentary.Analysis with both completed and imputed data found significant differences between PV and PS favouring the experimental group. The effect sizes were large for both threat appraisal constructs when completed data were used (see Turning to intention, analysis within completed data revealed non-significant treatment by time interaction effect. An inspection of the data shows a positive change in intention to reduce vaping use for the PMT intervention group when compared to the attention control group (With respect to vaping use, we found inconsistent and thus less convincing evidence for the effectiveness of the PMT intervention (see (Complete data) mean and standard error scores between treatment groups across time for PV, PS, intention, and behaviour.T0: Baseline; T1: Day 7; T2: Day 30; T3: Day 45.Overall, we found consistent treatment effects for both completed and imputed data sets. Nevertheless, there was a noticeable discrepancy in effect size among the variables of interest between the completed and imputed data sets. We would conclude with completed data that the effects were large (with the exception of intention which was medium) among the variables of interest. In contrast, we would conclude with imputed data that the effects were medium.With respect to theoretically driven relationships among the variables of interest, we found evidence that increases in the threat components of PV and PS were associated with reductions in intentions to vape. Amongst both data sets, bivariate correlation analysis revealed that PV corroborated strongest with vaping intention overall (There are several strengths to the present study. These include a factually based threat appraisal vaping intervention grounded in PMT that is both cost effective and scalable (i.e., online intervention that can be easily implemented in public and private health settings with limited financial or structural obstacles). This study is not without limitations. For instance, although missing data were at random and appropriate imputation procedures (i.e., multiple imputation) were followed, there were large amounts of missing data, particularly from baseline to time 1 (T1). Future studies should consider implementing more user-friendly survey design features (i.e., restricting participants from submitting their questionnaires before answering each question) to mitigate missing data. Considering the medium to large effect sizes found in the present study, future studies should also aim to recruit over 50 participants per group for a between treatment design with an α level of 0.05 and a power of 0.80 (