Timeline follow-back versus global self-reports of tobacco smoking: a comparison of findings with nondaily smokers.

Methods assessing nondaily smoking are of concern because biochemical measures cannot verify self-reports beyond 7 days. This study compared 2 self-reported smoking measures for nondaily smokers. A total of 389 college students (48% women, 96% White, mean age=19 years) smoking between 1 and 29 days out of the past 30 completed computer assessments in 3 cohorts, with the order of administration of the measures counterbalanced. Values from the 2 measures were highly correlated. Comparisons of timeline follow-back (TLFB) with the global questions for the total sample of nondaily smokers yielded statistically significant differences (p<.001), albeit small, between measures with the TLFB resulting on average in 2.38 more total cigarettes smoked out of the past 30 days, 0.46 fewer smoking days, and 0.21 more cigarettes smoked per day. Analyses by level of smoking showed that the discordance between the measures differed by frequency of smoking. Global questions of days smoked resulted in frequent reporting in multiples of 5 days, suggesting digit bias. Overall, the 2 measures of smoking were highly correlated and equally effective for identifying any smoking in a 30-day period among nondaily smokers. Copyright (c) 2009 APA, all rights reserved.