The biggest problem with Stan's approach is that when you examine e-cigarette users who are not using the product to quit, you are introducing a huge sampling bias. For example, why might someone use e-cigarettes, but not to quit? Most likely, the majority of vapers who are using e-cigarettes for a purpose other than cessation are using e-cigarettes to cut down on the amount they smoke. They are likely to derive benefits from smoking reduction. However, they are almost assuredly not going to quit smoking because they are not trying to quit, nor do they have such a desire.

The authors of this study make one of the most cardinal errors in all of epidemiology. They ignore the principle that "correlation does not equal causation."

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