Re: E-cigarette use and associated changes in population smoking cessation: evidence from US current population surveys
Zhu et al.  report an increase in quit attempts and smoking cessation rates in the United States (US) between 2010 and 2014, which confirms findings from a recent analysis of another population survey in the US . This is excellent news for all those concerned with public health. However, identifying the reasons behind this increase is a much more complex issue, as there may be other factors influencing intention to quit and success of quit attempts.
The authors mention price increases and national media campaigns that took place during the study period, but argue that they cannot fully explain the reported changes . While this might be true, there are multiple other factors that may have influenced smoking behaviour at the population level. Past year quit attempts and recent cessation have been found to be associated with age, ethnicity, education and health insurance in the United States . Thus, changes in any of the above factors could have had an impact on population-level cessation rates; Zhu et al. have only provided unadjusted estimates. Admittedly, sociodemographic changes are gradual and could only have a moderate impact between 2010 and 2014. On the contrary, this period coincides with the implementation of the Affordable Care Act, which increased health insurance coverage among US adults  and required improved smoking cessation provisions . This is reflected in the sharp increase of the proportion of smokers who received advice to quit tobacco from a health professional in the past year between 2010 and 2015 . Even brief advice from health professionals is known to increase smoking cessation .
More importantly, the authors state that “e-cigarette use itself could be an indicator of motivation to quit smoking, which would predict a higher quit rate” , but have not explored this further. E-cigarettes are heavily promoted as aids to quit smoking  and up to two thirds of e-cigarette users try e-cigarettes exactly because they aim to reduce or quit smoking . Therefore, e-cigarette users are likely to differ from non-users in terms of intention to quit; the study also reported that they differ in terms of sex, age, ethnicity and education, but this was not considered in the interpretation of the findings.
Overall, it is indeed likely that the availability of e-cigarettes encourages more smokers to try to quit smoking and this study is a useful addition to the relevant literature. However, it cannot provide strong evidence regarding the effect of e-cigarettes on smoking cessation at a population level. Unfortunately, this is how media have interpreted this publication. A moderate interpretation of study findings is increasingly difficult as the debate on e-cigarettes has become so polarised.
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Competing interests: No competing interests