Note that falsely reporting no smoking (i.e., no cigarettes) over the prior 24hr, when smoking had in fact occurred, would be expected selleck chem inhibitor to overestimate the optimum CO to verify abstinence since such subjects would be counted as quit despite high CO levels. For these 261 subjects, CO and cigarette tallies were assessed on a total of 2,572 days, with abstinence (0 cigarettes) identified during 1,012 days (39.4%), and nonabstinence (>0 cigarettes) identified during the remaining 1,560 days. Total days comprised 1,378 from the patch study, involving 563 abstinent (40.9%) and 815 nonabstinent days, and 1,194 days from the varenicline study, involving 449 abstinent (37.6%) and 745 nonabstinent days. A tally and/or a CO reading was missing for a total of 38 days, or 1.

6% of the total possible (2,610 days), from a total of 30 subjects. (Three other potential participants, or 1.1%, were excluded from all analyses due to repeated noncompliance with tally recording, as defined by CO > 10 ppm despite tallies indicating 0 cigarettes in the prior 24hr during three or more sessions.) This method has been shown to be valid and reliable in assessments of daily nicotine nasal spray medication use (Perkins et al., 1996). Statistical Analysis Consistent with prior research (e.g., Cropsey, Eldridge, Weaver, Villalobos, & Stitzer, 2006; Javors et al., 2005), sensitivity was determined by the percentage of CO values that were above the designated criterion for abstinence (e.g., above 4 ppm, above 8 ppm) on the days in which at least one cigarette (>0) was smoked during the prior 24hr.

Similarly, specificity was determined by the percentage of CO values below the abstinence criterion on the days in which zero cigarettes were smoked in those prior 24hr. To further compare subgroups on how well CO discriminated between abstinent and nonabstinent days, we assessed the area under the curve (AUC) for the receive-operator characteristics (ROC), using the nonparametric method (Zweig & Campbell, 1993). To do so, we plotted sensitivity by specificity for all obtained CO levels, with AUC of 1.0 indicating perfect identification of abstinence and nonabstinence and 0.5 demonstrating no discrimination between the two (see Javors et al., 2005). Nonoverlapping 95% confidence intervals (CIs) for AUC values indicated subgroup differences.

RESULTS Over the AV-951 two 5-day quit attempt periods, the mean �� SD number of abstinent and nonabstinent days was 3.9��3.6 versus 6.0��3.6, respectively. Corresponding mean CO values were 3.2��2.2 versus 12.3��7.3 ppm, respectively. In the ROC analysis, AUC �� SEM was 0.910 �� .006, p < .001, with a 95% CI of 0.899�C0.921, showing very strong ability of CO to discriminate between days of smoking (sensitivity) and abstinence (specificity), as expected. More importantly, a CO criterion of 5 ppm for smoking (i.e.