The introduction and proliferation of filtered cigarettes occurred mostly in the decades preceding and following the 1964 Surgeon General's report and was mostly complete by 1974. Further reductions in tar yield occurred through other mechanisms, as by 1974, most cigarette brands were filtered.

This argument is fallacious, I believe, because there are many things that changed from one cohort to the next. The introduction of cigarette filters is only one such change. To assume that any observed changes in cancer risk from one cohort to the next must be attributable to one particular change - the filter - is not appropriate, in my view.

• We lied to you when we told you that "No studies have been done to examine the safety of e-cigarettes."

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