2. Those products are not electronic (fake) cigarettes.

"Analysis of indoor air quality during vaping sessions showed that e-cigarettes are not emission-free." This was the second time the authors used this phrasing to summarize their findings. Right now, that e-cigarettes are not emission free appears to be about the most alarming thing that can be said about them.

The problem is that in this cross-sectional study, there is no way to determine the direction of the observed relationship.

Here, they find a correlation between e-cigarette use and higher and more sustained levels of smoking. But because this is a cross-sectional study, they cannot determine which came first. In other words, what is the direction of the causal relationship? Does the e-cigarette use precede, and cause, the smoking? Or does the smoking precede, and cause, the e-cigarette use?

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