The phenotypic outcome measure used in the logistic regression analyses is relapse, which is defined as re-engaging in smoking after quitting for one week or longer. Relapse was used as the dependent variable while the Rasch modeled nicotine withdrawal sensitivity score was the independent variable in the logistic regression analysis. The phenotypic outcome measure used in the linkage and association analyses is the nicotine withdrawal sensitivity score formulated using the smoking withdrawal responses from the Smoking History Questionnaire with details of the development of this measure described in (22). The unidimensional nicotine withdrawal sensitivity score summarizes the eight quit attempt symptoms. The nicotine withdrawal sensitivity score was examined for autosome-wide linkage and for candidate gene association with SNPs of the OPRM1 gene.
