Median IPI values were compared with the Wilcoxon two-sample test. Analyses were performed using SAS Proc Mixed selleck chemicals procedure. p Values less than .05 were considered to be statistically significant. Bonferroni corrections were applied to adjust for Type I error rates resulting from multiple comparisons, as appropriate. Generalized estimating equations, using SAS Proc Genmod, were used to examine which group (SS vs. CON) was more likely to have IPIs ��6 and ��10 s. We used random effects logistic regression analyses to compare differences between rapid smoking and non-rapid smoking groups. All statistical analyses were performed using SAS v. 9.1. Results Characteristics of the Sample Baseline clinical and sociodemographic data for the sample are described in Table 1.
SS were older and more likely to be men compared with CON (both p < .01). Although both groups smoked the same average number of cigarettes per day, SS had higher baseline expired CO (23.1 vs. 19.5; p < .05). On other characteristics including FTND total score, age of first smoking, number of past quit attempts, race/ethnicity, and education, there were no differences between groups. Serum nicotine and cotinine levels were significantly higher in SS compared with CON (31.3 vs. 24.4 ng/ml and 450.9 vs. 303.9 ng/ml, respectively; both p < .001). Mean 3HC/cotinine ratios were not different between groups (mean 0.54 vs. 0.49; p = .49). Table 1. Characteristics of the Sample Rapid Smoking As reported in Williams et al. (2011), SS differed significantly from CON on measures of smoking topography.
During the assessment period, data from 38,691 individual puffs (2,966 total cigarettes) were collected. SS smoked an average of 2.8 more puffs per cigarette than CON (both p < .001) in addition to smoking more cigarettes in the 24-hr testing session (mean 21.0, SS vs. 16.0, CON). The mean time between puffs or IPI was significantly shorter in SS (16.0 vs. 22.6 s; p < .001). Due to the skewed distribution of the data, we also examined the median IPI and found that it was shorter in SS than CON (9.3 vs.15.7 s; p < .001; Figure 1). Average total time to finish smoking a cigarette was shorter in SS compared with CON (4.5 vs. 5.5 min; p < .001). Figure 1 Distribution of interpuff interval scores. We examined the frequency of IPIs ��6 s. SS were twice as likely to have IPIs ��6 s than CON (OR = 2.32, 95% CI = 1.68, 3.20; p < .001). SS were also more likely to have IPIs Brefeldin_A ��10 when compared with CON (OR = 2.69, 95% CI = 2.24, 3.22; p < .001).