Discussion
depression, depressive symptoms, depressed, tobacco dependence
REGRESSION
Among users of a smartphone app for smoking cessation who participated online in a randomised trial testing the effectiveness of this app, smoking cessation after 6 months was predicted primarily by the degree of tobacco dependence (cigarettes/day and minutes to first cigarette), by the degree of motivation to quit smoking, by the frequency and duration of use of the app and its perceived usefulness, and by the use of nicotine medication.Among those who continued to smoke after 6 months, reduction in the number of cigarettes/day was mainly predicted by level of tobacco dependence (cigarettes/day and minutes to first cigarette), use of nicotine medication, frequency of app use and its perceived usefulness, and use of e-cigarettes. The reduction in the number of cigarettes per day over time was greatest among those who had smoked more cigarettes per day at baseline, but this may reflect a phenomenon of regression to the mean [Among those who had quit smoking after one month, relapse to smoking after six months was mainly predicted by intention to quit, frequency and intensity of app use, perceived usefulness of the app, level of dependence and use of nicotine medication.Being in the experimental group (compared to the control group) was not a predictor of smoking status or smoking reduction at 6 months, but it did increase the likelihood of nicotine medication use, as previously reported [The importance of tobacco dependence, motivation to quit smoking, and nicotine therapy as predictors of smoking cessation, smoking reduction and relapse is well documented [The causality can go both ways: either more frequent use of the app increased the likelihood of quitting or reducing smoking, or those who quit had withdrawal symptoms and therefore needed more support and consequently used the app more often. According to the Self-determination theory, participants might also need and possibly found more support in the app, in the form of relationships (discussion forum) and behaviour change skills, regardless of withdrawal symptoms [In addition, both smoking cessation/reduction and app use may be influenced by other factors (e.g. motivation, social support and social pressure, environmental factors) that may contribute to the present results.The association between frequency of app use and smoking cessation or reduction was also observed among control app users, either supporting the latter two explanations or suggesting that the control app was effective despite its limited content.Although these correlational analyses cannot prove causality, they can help us formulate hypotheses that can later be tested experimentally. For example, the effectiveness of the app could be improved if it included additional features that increased the frequency or duration of use, and user satisfaction, e.g. by expanding the existing social network within the app to make it more active or supportive (the user would then open the app more frequently to read or post messages and receive encouragement from peers), or by further developing the existing customised feedback support system to make it more intensive or more timely (e.g., ensuring that automated, individualised messages are available during a relapse episode or during episodes of craving and other withdrawal symptoms), or the app could also be improved if it further increased participants’ use of nicotine medications, or if it increased their use of external supports such as smoking cessation services and local clinics.The association between heated tobacco use and smoking cessation after adjustment for other predictors yields a hypothesis that should be tested experimentally [Incidentally, most of the study participants tested positive for depression, and depressed participants were less likely to quit smoking after six months than non-depressed participants. This result is consistent with other studies showing that patients who come to a smoking cessation clinic with depressive symptoms are less likely to quit smoking than patients without such symptoms [Finally, in the current study, men were more likely to reduce their cigarette consumption than women. This finding is consistent with recent studies showing that withdrawal symptoms are more pronounced in female smokers than in male smokers and that female smokers are more likely to relapse than male smokers [