E-cigs can increase odds for smokers using them to quit while still having overall negative effect on population quitting

Robert West and colleagues just published a large population-based cross-sectional study of the relationship between e-cigarette use and having stopped using cigarettes in England that shows that, among smokers who made at least one quit attempt in the last year, smokers who used ecigs as part of their quit attempt were statistically significantly more likely to no longer be smoking cigarettes than smokers who used unassisted NRT or no aids.
 
Subject to all the usual caveats about cross-sectional studies, this is a reasonably done study for what it claims to compare.  The use of statistical methods to adjust for differences between the groups is the standard way to analyze such real world studies.  Like others, they found that the adjustments did not change the results very much.
 
I agree with West that, for mass-marketed products like e-cigarettes, this kind of real-world study is more meaningful than randomized clinical trials.
 
It is important, when interpreting their findings, to remember what they studied:  They limited themselves to people who were using ecigs as part of quit attempts.
 
This is different than looking at the effects of ecig use on quitting among all ecig users, as the studies that we reviewed in our recent paper in Circulation did.  This is an important distinction because all the studies so far of all smokers and ecigs show about 1/3 lower quitting among ecig users.
 
The effects that are estimated in studies of all smokers are the combined effects of ecigs on (1) the likelihood that ecigs promote or inhibit quit attempts and, (2) the likelihood that people using ecigs to quit are successful.
 
The West paper looks at the second step of this process.
 
Putting all 6 studies together (the 5 we reviewed plus West's study) suggests that ecigs both discourage quit attempts among smokers in general but increase success for the (smaller number of) people who use them to quit, resulting in a net negative effect of the presence of e-cigs on overall quitting in the population. 
 
West has the data to address this question; all he needs to do is run the same analysis he did using all the smokers, not just those that made quit attempts.  (He could also estimate the association of e-cigarette use with making a quit attempt.)  When the New York Times asked him about this point, he said he was conducting additional analysis.  I'm surprised that he didn't include this information in the paper (since it would have been just one more computer run with his existing models).  Hopefully he will publish that result soon.
 
In addition, it would be worth publishing the results of the comparison of ecigs with NRT plus counseling as well as with the other forms of FDA approved cessation therapies.  While the comparison in the paper is informative, one normally compares treatments with best practices.  This is also something he could easily run with the data at hand.