As is so often the case, the answer is money.

The authors admit this in the paper. They write: "This is a cross-sectional study, which only allows us to identify associations, not causal relationships."

What the study found was that 11.9% of the former smokers had ever tried an electronic cigarette in the past year. This means they might have tried an electronic cigarette once and never taken another puff again. It means they may have tried a single puff on an electronic cigarette just to see what it was like.

One might argue that this is just one errant professor. However, as it acknowledges on its :

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