On 2017 Feb 18, Clive Bates commented:

Erroneous interpretations have been placed on these results and overly confident conclusions drawn from very small numbers of imperfectly characterised teenagers. The headline recommendations were based on the behaviour of six out of 16 baseline e-cigarette users in a sample of 694 adolescents deemed not to be susceptible to smoking. Large conclusions drawn from small numbers should always be a cause for caution, as discussed in this article about this study by Five Thirty-Eight:

Ignore The Headlines: We Don’t Know If E-Cigs Lead Kids To Real Cigs by Christie Ashwandan, 11 September 2015

One should expect the inclination to use e-cigarettes to be caused by the same things that cause an inclination to smoke - they are similar habits (the former much less risky) and it is quite likely that those who used e-cigarettes first would have become smokers first in the absence of e-cigarettes - a concept known as shared liability. A range of independent factors that create a common propensity to smoke or vape, such as parental smoking, rebellious nature, delinquency etc. explain the association between vaping and smoking incidence but without this relationship being causal.

The authors try to address this by characterising teenagers non-susceptible to smoking if they answer “definitely no” when asked the following: “If one of your friends offered you a cigarette, would you try it?” and “Do you think you will smoke a cigarette sometime in the next year?”. The study concentrates on this group.

This is not a foolproof way of characterising susceptibility to smoking, which in any case is not a binary construct but a probability distribution. Nor is susceptibility a permanent condition for any young person - for example, if a teenage girl starts seeing a new boyfriend who smokes that will materially changes her susceptibility to smoking. The fact that some were deemed unsusceptible to smoking but were already e-cigarette users is grounds for further unease - these would be more likely to be the teens where the crude characterisation failed.

It is a near-universal feature of tobacco control research that the study presented is a wholly inadequate basis for any policy recommendation drawn in the conclusion, and this study is no exception:

These findings support regulations to limit sales and decrease the appeal of e-cigarettes to adolescents and young adults.

The findings do not support this recommendation, not least because the paper is concerned exclusively with the behaviour of young people deemed not susceptible to smoking and, within that group, a tiny fraction who progressed from vaping to smoking. Even for this group (6 of 16) the authors cannot be sure this isn't a result of mischaracterisation and that they would not have smoked in the absence of e-cigarettes. The approach to characterising non-susceptibility is far too crude and the numbers involved far too small to draw any policy-relevant conclusions.

But this isn't the main limitation. Much more troubling is that the authors made this policy recommendation without considering the transitions among young people who are susceptible to smoking - i.e. those more likely to smoke, and also those much more likely to use e-cigarettes as well as or instead of smoking. This group is much more likely to benefit from using e-cigarettes as an alternative to smoking initiation, to quit smoking or cut down or as a later transition as they approach adult life.

There are already findings (Friedman AS, 2015, Pesko MF, 2016, Pesko MF, Currie JM, 2016) that regulation of the type proposed by the authors designed to reduce access to e-cigarettes by young people has had unintended consequences in the form of increased smoking - something that should not be a surprise given these products are substitutes. While one may debate these findings, the current study makes no assessment of such effects and does not even cover the population that would be harmed by them. With these limitations, it cannot underpin its own over-confident and sweeping policy recommendation.

On 2017 Feb 18, Clive Bates commented:

Erroneous interpretations have been placed on these results and overly confident conclusions drawn from very small numbers of imperfectly characterised teenagers. The headline recommendations were based on the behaviour of six out of 16 baseline e-cigarette users in a sample of 694 adolescents deemed not to be susceptible to smoking. Large conclusions drawn from small numbers should always be a cause for caution, as discussed in this article about this study by Five Thirty-Eight:

Ignore The Headlines: We Don’t Know If E-Cigs Lead Kids To Real Cigs by Christie Ashwandan, 11 September 2015

One should expect the inclination to use e-cigarettes to be caused by the same things that cause an inclination to smoke - they are similar habits (the former much less risky) and it is quite likely that those who used e-cigarettes first would have become smokers first in the absence of e-cigarettes - a concept known as shared liability. A range of independent factors that create a common propensity to smoke or vape, such as parental smoking, rebellious nature, delinquency etc. explain the association between vaping and smoking incidence but without this relationship being causal.

The authors try to address this by characterising teenagers non-susceptible to smoking if they answer “definitely no” when asked the following: “If one of your friends offered you a cigarette, would you try it?” and “Do you think you will smoke a cigarette sometime in the next year?”. The study concentrates on this group.

This is not a foolproof way of characterising susceptibility to smoking, which in any case is not a binary construct but a probability distribution. Nor is susceptibility a permanent condition for any young person - for example, if a teenage girl starts seeing a new boyfriend who smokes that will materially changes her susceptibility to smoking. The fact that some were deemed unsusceptible to smoking but were already e-cigarette users is grounds for further unease - these would be more likely to be the teens where the crude characterisation failed.

It is a near-universal feature of tobacco control research that the study presented is a wholly inadequate basis for any policy recommendation drawn in the conclusion, and this study is no exception:

These findings support regulations to limit sales and decrease the appeal of e-cigarettes to adolescents and young adults.

The findings do not support this recommendation, not least because the paper is concerned exclusively with the behaviour of young people deemed not susceptible to smoking and, within that group, a tiny fraction who progressed from vaping to smoking. Even for this group (6 of 16) the authors cannot be sure this isn't a result of mischaracterisation and that they would not have smoked in the absence of e-cigarettes. The approach to characterising non-susceptibility is far too crude and the numbers involved far too small to draw any policy-relevant conclusions.

But this isn't the main limitation. Much more troubling is that the authors made this policy recommendation without considering the transitions among young people who are susceptible to smoking - i.e. those more likely to smoke, and also those much more likely to use e-cigarettes as well as or instead of smoking. This group is much more likely to benefit from using e-cigarettes as an alternative to smoking initiation, to quit smoking or cut down or as a later transition as they approach adult life.

There are already findings (Friedman AS, 2015, Pesko MF, 2016, Pesko MF, Currie JM, 2016) that regulation of the type proposed by the authors designed to reduce access to e-cigarettes by young people has had unintended consequences in the form of increased smoking - something that should not be a surprise given these products are substitutes. While one may debate these findings, the current study makes no assessment of such effects and does not even cover the population that would be harmed by them. With these limitations, it cannot underpin its own over-confident and sweeping policy recommendation.