Although the survey approach described above would lead to "invalid" results, I would never argue that survey studies should be thrown out and that we should only be conducting RCTs. My point is that there are strengths and limitations of various study designs, and causal inference is enhanced by having research evidence from multiple study designs. On balance, the strengths and weaknesses balance each other out, leading to a much greater ability to draw valid conclusions.

"Only 1.8% of children are regular users; 90% of regular or occasional users are young people who are already smokers or ex-smokers; 91% of young people have not tried an electronic cigarette even once; and this is despite the fact that over 80% of young people are now aware of e-cigarettes (up from under 70% in 2013)."

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