Nicotine dependence was defined conditionally, such that (a) lifetime DSM-IV ND items were combined into a seven-item symptom count for respondents who endorsed having ever used cigarettes, and (b) abstainers were coded as missing. Following Lessov and colleagues (2004), tolerance to nicotine was operationalized as having ever smoked 20 or more cigarettes in one day. The normality parameters for the symptom count were within acceptable limits (skewness=0.62, kurtosis=−1.01). The number of ND symptoms ranged from 0 to 7 in men (M=1.85, SD=1.97) and women (M=1.65, SD=1.96) and the average number of symptoms in the sample was 1.74 (SD=1.97). The lifetime prevalence of ND among men, women, and the sample was 35.2%, 30.3%, and 32.3%, respectively. The symptom count demonstrated good internal consistency reliability (Cronbach’s α=0.81) and good test-retest reliability (r(147)=.84, p<.0001). It was correlated modestly with birth year (r=−.06) and assessment year (r=−.06).
