Chicago’s Department of Public Health (CDPH) promoted a National Institutes of Health-funded (NIH) study Wednesday that shows teens using e-cigarettes are more likely to start smoking tobacco.

The study, published in 2015, examined 9th grade students in Los Angeles and found those who had tried e-cigarettes were 2.7 times more likely to initiate smoking than their peers.

On the surface, these findings appear to back-up the CDPH’s hyperbolic tweet. But the study itself is full of drawbacks that make the CDPH’s claim look like an overreaction at best and a willful misrepresentation at worst. (RELATED: Fact Check: Rahm Emanuel’s Spin Fueled Campaign Against E-Cigarettes)

NIH study shows “Teens Using E-cigarettes More Likely to Start Smoking Tobacco” https://t.co/x4BR5BHofO #VapingTruth — ChiPublicHealth (@ChiPublicHealth) January 6, 2016

Dr. Michael Siegel, a Professor in the Department of Community Health Sciences, Boston University School of Public Health, points out in his blog post from August 2015, “the study did not measure ‘e-cigarette use.’ It merely asked kids whether they had ‘ever’ tried an e-cigarette. Kids who had ever tried an e-cigarette, even a puff, were compared with all kids who had never even puffed on an e-cigarette.”

This represents a problem when attributing the causality of smoking to e-cigarettes. “Kids who would not even try an e-cigarette, despite their popularity, represent a different population than kids who would try a puff on an e-cig,” says Siegel.

The fact that the children who wouldn’t experiment with even a puff of an e-cigarette are less likely to try regular tobacco should come as no surprise. The former Director of Action on Smoking and Health Clive Bates, agrees with Siegel:

Adolescents who use e-cigarettes may be more likely to begin smoking, but not necessarily because they used e-cigarettes. The most likely explanation is that whatever it is that inclines young people to smoke (actually to experiment), also inclines them to use e-cigarettes.

The study also failed to record whether any of the subjects were regular vapers and had a nicotine addiction before they experimented with cigarettes. The only fact the study could muster is that some of the subjects had tried an e-cigarette at some point. Nowhere does the study claim regular users of e-cigarettes transitioned to smoking tobacco.

This fact directly clashes with CDPH’s claim that “teens using e-cigarettes more likely to start smoking tobacco.”

Another big problem for those who want to make the link between e-cigarette use and smoking, is that the study defined smoking as any cigarette use, no matter how small. So among the subjects who tried cigarettes, we have no idea whether any of them are actually regular or even semi-regular smokers, if they are smoking at all.

The editorial accompanying the study readily acknowledges this fact:

Because the only outcome measure was any use of a tobacco product during the past six months, the analysis could not distinguish students who had just tried a few cigarettes from those who progressed to regular smoking during follow-up. The latter is the greater concern, and the current study cannot determine whether e-cigarette exposure was associated with that outcome.

The study’s own authors even went so far as to say, “we cannot conclude that e-cigarette use directly leads to smoking.”

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