On 2017 Sep 18, Clive Bates commented:

The paper provides a very unsatisfactory contribution to the literature on e-cigarettes and harm reduction, from which no useful policy conclusions can be drawn.

CONCLUSIONS: E-cigarette use, which is common in adults with or at risk for COPD, was associated with worse pulmonary-related health outcomes, but not with cessation of smoking conventional cigarettes. ​

But it turns out that e-cigarette use was associated with more intensive smoking in the past.

E-cigarette users had a heavier conventional cigarette smoking history and worse respiratory health, were less likely to reduce or quit conventional cigarette smoking, had higher nicotine dependence, and were more likely to report chronic bronchitis and exacerbations.

This likely explains the difference in respiratory health and why more heavily dependent users may find it harder to quit. In other words, it is nothing to do with e-cigarettes, the use of which is probably just a marker of more intensive smoking, higher dependency and greater difficulty quitting - not caused by e-cigarette use. It is the smoking history that matters.

From this the authors add to their conclusion:

Although this was an observational study, we find no evidence supporting the use of e-cigarettes as a harm reduction strategy among current smokers with or at risk for COPD.

​It is literally true that they "find no evidence...", but that is because this study is completely ill-suited to drawing any policy conclusions about e-cigarettes and COPD. Despite hinting at the limitations of cross-sectional data, the authors draw a negative-sounding conclusion without addressing the key question of how respiratory health changes for a given smoker who uses e-cigarettes to quit or cut down once they are ill from smoking or as a way of preventing COPD.

For respiratory physicians wondering what to do in the interest of their patients, Polosa R, 2016 Evidence for harm reduction in COPD smokers who switch to electronic cigarettes might be more useful.

A whole new level of over-interpretation is achieved in the press statements that accompany this paper.

"The data further suggest that there's no clear benefit of e-cigarettes as a harm-reduction strategy in this population of smokers with or at-risk for COPD."

This effortlessly moves from a no-evidence-of-effect (the paper) to evidence-of-no-effect (the press statement). I'm sure the authors will be embarrassed by that.

On 2017 Sep 18, Clive Bates commented:

The paper provides a very unsatisfactory contribution to the literature on e-cigarettes and harm reduction, from which no useful policy conclusions can be drawn.

CONCLUSIONS: E-cigarette use, which is common in adults with or at risk for COPD, was associated with worse pulmonary-related health outcomes, but not with cessation of smoking conventional cigarettes. ​

But it turns out that e-cigarette use was associated with more intensive smoking in the past.

E-cigarette users had a heavier conventional cigarette smoking history and worse respiratory health, were less likely to reduce or quit conventional cigarette smoking, had higher nicotine dependence, and were more likely to report chronic bronchitis and exacerbations.

This likely explains the difference in respiratory health and why more heavily dependent users may find it harder to quit. In other words, it is nothing to do with e-cigarettes, the use of which is probably just a marker of more intensive smoking, higher dependency and greater difficulty quitting - not caused by e-cigarette use. It is the smoking history that matters.

From this the authors add to their conclusion:

Although this was an observational study, we find no evidence supporting the use of e-cigarettes as a harm reduction strategy among current smokers with or at risk for COPD.

​It is literally true that they "find no evidence...", but that is because this study is completely ill-suited to drawing any policy conclusions about e-cigarettes and COPD. Despite hinting at the limitations of cross-sectional data, the authors draw a negative-sounding conclusion without addressing the key question of how respiratory health changes for a given smoker who uses e-cigarettes to quit or cut down once they are ill from smoking or as a way of preventing COPD.

For respiratory physicians wondering what to do in the interest of their patients, Polosa R, 2016 Evidence for harm reduction in COPD smokers who switch to electronic cigarettes might be more useful.

A whole new level of over-interpretation is achieved in the press statements that accompany this paper.

"The data further suggest that there's no clear benefit of e-cigarettes as a harm-reduction strategy in this population of smokers with or at-risk for COPD."

This effortlessly moves from a no-evidence-of-effect (the paper) to evidence-of-no-effect (the press statement). I'm sure the authors will be embarrassed by that.