RE: Effectiveness of Pharmaceutical Smoking Cessation Aids in a Nationally Representative Cohort of American Smokers

We read with interest Leas et al.'s analysis of the Current Population Survey data (1) relating the use of pharmacotherapy to outcome in attempts to quit smoking, particularly as a decade ago we published a similar analysis on some of the same data (2), not cited by Leas et al. We strongly agree with the editorial by Tindle and Greevy that a major issue in the analysis is serious confounding when treatment is assigned clinically or self-selected (3). This is a classic case of the well-known "confounding by indication" (4,5) (or by "severity") problem, in which treatment is primarily used by those who already have the most severe conditions and are the most prone to poor outcomes. Leas et al. undertook heroic efforts to overcome confounding by propensity score matching, but this is insufficient to remove this bias. Those who are convinced they cannot succeed without treatment (and perhaps whose doctors are also so convinced) are most likely to use it. The limited data available in the survey cannot account for all the factors that may enter into smokers' assessment of their own prognosis (eg, how motivated they are to quit, how difficult they found quitting last time they tried, what impediments to quitting they expect, etc.). When treatment is actively "assigned" by assessed of risk of failure, the resulting bias is near impossible to correct (5).

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