More evidence that e-cigs are depressing quitting smoking in the real world

Erin Sutfin and colleagues at Wake Forest University just published “ The Impact of Trying Electronic Cigarettes on Cigarette Smoking by College Students: A Prospective Analysis” in American Journal of Public Health that adds to the evidence that e-cigarette use is depressing quitting smoking cigarettes.
This paper follows several hundred college students over 3 years during which time they assessed smoking behavior, how often respondents smoked (a measure of nicotine dependence) other tobacco use, and a variety of personality and demographic characteristics.  Controlling for all these factors, the authors found that among young adults who were smoking at baseline, e-cigarette use was associated with higher likelihood of smoking at follow-up.
Here is the abstract:

Objectives. We assessed the impact of trying e-cigarettes on future cigarette smoking in a sample of college student smokers.
Methods. In this longitudinal study, first-semester college students at 7 colleges in North Carolina and 4 in Virginia completed a baseline survey and 5 follow-up surveys between fall 2010 and fall 2013. Current cigarette smoking at wave 6 was the primary outcome. Participants (n = 271) reported current cigarette smoking at baseline and no history of e-cigarette use. We measured trying e-cigarettes at each wave, defined as use in the past 6 months.
Results. By wave 5, 43.5% had tried e-cigarettes. Even after controlling for other variables associated with cigarette smoking, trying e-cigarettes was a significant predictor of cigarette smoking at wave 6 (adjusted odds ratio [AOR] = 2.48; 95% confidence interval [CI] = 1.32, 4.66), as was friends’ cigarette smoking (AOR = 4.20; 95% CI = 2.22, 7.96) and lifetime use of other tobacco products (AOR = 1.63; 95% CI = 1.22, 2.17).
Conclusions. Trying e-cigarettes during college did not deter cigarette smoking and may have contributed to continued smoking. (Am J Public Health. Published online ahead of print June 11, 2015: e1–e7. doi:10.2105/AJPH.2015.302707)

Put in terms of the odds of quitting, use of e-cigarettes is associated with reduced quitting with an adjusted odds ratio of 0.40 (95% CI 0.21-0.76), consistent with the overall findings of the rest of the studies of the effects of e-cigarette use on quitting conventional cigarettes.
This is, of course, good news for the multinational cigarette companies, which are increasingly dominating the e-cigarette business.


Great quote from Discussion section

"These findings suggest that for college students smokers, trying e-cigarettes and, in particular, repeated e-cigarette use is a predictor of continued cigarette smoking."

Again, this is subject to reverse causality

This is subject to reverse causality; those who quit naturally are less lkely to subsequently experiment with ecigs. Furthermore, ever-use is such a week measure that it's very hard to weed out the confounding.
Furthermore, observational studies find negative associations with approved cessation aids as well, because of confounding and reverse causality

Reverse causality is not an issue in longitudinal studies

... because the stimulus (in this case e-cigarette use) is measured before the outcome (continued smoking at a later point in time).
The study you cite is a cross-sectional, not a longitudinal, study.

this is unfair, you responded but did not post my response

this is unfair, you responded but did not post my response: if the stimulus was measured before the possible outcome than only dual users were included making this a biased sample.

The sample is appropriate.

The study compared quitting cigarettes among people who did (dual users) and did not use (cigarettes only) c-cigarettes concurrently with cigarettes at baseline.

Thanks very much for the clarification

Thanks for the clarification.
New question: now that I understand that those who had already quit by wave 5 were excluded (don't have full text), then there is considerable selection bias due to the fact that those who tried EC and quit cigarettes before wave 5 are excluded fom the ecig user sample.

Read the full paper

The paper is available.  You should read the whole thing rather than expect me to explain it to someone who has only read the abstract.  The paper is very carefully done using established methods.