Consistency of daily cigarette smoking amount in dependent adults

Self-reported cigarettes per day (CPD) is a very common screening as well as dependent or independent measure in clinical and nonclinical research on smoking, but the consistency of CPD across days in dependent smokers is uncertain. Adult dependent smokers (N = 357; 170 men, 187 women) retrospectively reported "usual" CPD at screening and then prospectively self-monitored CPD on 3 consecutive days of 1 week during an ad libitum baseline period. Participants were those recruited for later tests of brief medication effects in those with high (n = 170) versus low (n = 187) interest in quitting smoking soon (within 3 months). Consistency was determined by intraclass correlation (ICC). Prospective daily CPD was generally consistent (ICC = 0.78, 95% CI of 0.74-0.81), but CPD changed (increased or decreased) by 5 cigarettes/day or more in 40% of participants and by at least 10/day in 10%. Consistency in CPD was greater in higher dependent smokers and in women with low (vs. high) quit interest, but consistency tended to be greater in men with high (vs. low) quit interest. Although retrospectively reported CPD at screening was consistent with the overall mean for prospectively monitored daily CPD, 15% of participants differed by at least 5/day between methods, and digit bias was twice as likely with retrospective versus prospective CPD, which was at chance levels. Understanding variability in CPD may improve knowledge of dependence and factors that foster or discourage daily smoking amount, but precise assessment of daily CPD likely requires prospective monitoring.