For example, one of the major problems in some of the previous survey studies of electronic cigarettes (the ones cited by Stan Glantz, for example) is that they fail to control for a major confounder: the level of a smoker's addiction to smoking and motivation to quit. Some of the studies that Glantz has cited to show that e-cigarettes are ineffective for smoking cessation compare users of e-cigarettes and non-users of e-cigarettes. In two of these studies, those who did not use e-cigarettes had higher quit rates.

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