The problem with the majority of scientific studies (on smoking and any other currently PC taboo topic) is: the people conducting them start with their findings in mind prior to conducting their research. Once you know what you want to prove...the rest is easy!
Very true....and that applies across the board, even to methodologies used in education. Remember the "new math"? It bombed, despite the "scientific" evidence used to promote it as a great way to learn. And "whole language"? Another proven a failure, contrary to all the "scientific evidence" stating otherwise. Whole language only programs were such a failure that then California Gov. Davis REQUIRED phonics instruction be immediately returned to all its schools' curriculum once it was shown that CA students' reading scores were lowest in the entire nation, with the exemption of Guam.