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?

Second, in dual users, the total amount of nicotine intake declines. The increase in electronic cigarette use over time is accompanied by a concomitant decline in cigarette smoking. Thus, overall nicotine declines.

And predictably, the Campaign for Tobacco-Free Kids (CTFK) .

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