history and withdrawal symptoms (16). Specifically respondents were asked: ‘During the first few days after you quit smoking cigarettes (the first or the most recent time) for at least 3 months, did you feel or experience any of the following?’. Items, presented were: irritable or angry, restless, increased appetite, depressed mood, difficulty sleeping, craving to use tobacco, anxious, and difficulty concentrating. Previously (14), a withdrawal severity scale that included these eight symptoms of withdrawal, as well as a ninth symptom “decreased heart rate”, was used in a linkage analysis. The Rasch modeled nicotine withdrawal sensitivity score did not include the ninth withdrawal symptom due to reduced fit in a number of correlation, factor and item response analyses (data not shown). These analyses use the Rasch modeled nicotine withdrawal sensitivity score for analyses with relapse, defined as re-engaging in smoking after quitting for one week or longer, and for autosome-wide linkage analysis and association analysis with common variation at a candidate gene of importance for smoking behavior, the mu opioid receptor (MOR) gene (OPRM1).
