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.

After blasting electronic cigarettes, the author writes:

Some of the most important conclusions in epidemiologic research have come not from large case-control or cohort studies or clinical trials, but from case studies or case series, or as Dr. Frieden would say, "anecdotes."

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