Background and Aims:

Nicotine addiction theory predicts small day to day variability in cigarettes/day (CPD) whereas social learning theory predicts large variability. A description of the variability in CPD over multiple days is not available.

Methods:

We conducted secondary analyses of two natural history studies with daily smokers - one of smokers not intending to quit, and one of smokers intending to quit sometime in the next 3 months. In the former, smokers recorded their smoking during the day by Ecological Momentary Assessment, using a palm-top computer. In the latter, participants reported CPD nightly via a phone Interactive Voice Response system. Analyses were based on smokers who reported averaging > 10 CPD, and on days in which there was no attempt to stop or reduce smoking.

Results:

Across the two studies, on average, smokers had small changes in day-to-day CPD (mean changes were 2.2 and 2.9 CPD). However a minority averaged changing by > 5 CPD from one day to the next (7% and 11%), and many changed by > 5 CPD on at least 10 of the 90 days (8% and 31%). Neither smoking restrictions, dependence, stereotypy ratings, nor interest in quitting predicted variability.

Conclusion:

Although on average, smokers have little change day-to-day CPD, a substantial minority of smokers often change by 5 CPD from day-to-day. We did not find potential causes of this variability.

Implications:

Across day variability in CPD is larger than implied in prior studies. Determining causes of day to day variability should increase our understanding of the determinants of smoking.