Differences in age, education, and verbal IQ between the groups were not statistically significant (p>0.07, two-sample t-test). Similarly, the gender difference between groups was not statistically significant (p = 0.27; Fisher's exact test). There were also no significant differences in symptoms of depression, as assessed with the Beck Depression Inventory II edition [24], between the cocaine and control groups (p = 0.093; two-sample t-test). Fifteen cocaine subjects were cigarette smokers while only five control subjects were cigarette smokers; the difference in cigarette smoking between the groups was statistically significant (p = 0.004; Fisher's exact test). Subjects were allowed to smoke regularly to minimize withdrawal symptoms. Specifically, seven cocaine subjects smoked within 4 hours prior the study and 4 additional cocaine subjects smoked within 6 hours prior the study. There was no difference in time since last cigarette (within 4 hours, >4 hrs, overnight or more) or in smoking frequency between the groups (P>0.54 t-test). Nineteen cocaine subjects met DSM-IV diagnosis for cocaine dependence or abuse, and had at least a 12-month (4 days/week for all but one subject) history of
