Tobacco control
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To assess differences in demographic and smoking characteristics between smokers who have and have not used nicotine replacement therapy (NRT). ⋯ Smokers who elect to use NRT differ from non-NRT users in ways that predispose them to failure in cessation. Controlling for smoking rate and time to first cigarette does not eliminate these differences, even among light smokers. These differences must be considered when comparing the effectiveness of NRT among samples of smokers who self select their treatment and are likely to bias such outcome comparisons.