Do point prevalence and prolonged abstinence measures produce similar results in smoking cessation studies? A systematic review.

INTRODUCTION: Many smoking cessation trials report either prolonged abstinence (PA) rates (i.e., not smoking since a quit date, with or without a grace period) or point prevalence (PP) abstinence rates (i.e., no smoking one or more days prior to the follow-up), but how these two relate is unclear.
METHODS: We located 28 pharmacotherapy trials that provided 76 within-study comparisons of PA versus PP. The first two authors independently coded all trials.
RESULTS: The two measures were highly correlated (r = .88) and PA averaged 0.74 that of PP. Equations for converting PP to PA and vice versa produced estimations that, in 90% of cases, were within 4%-5% of actual PP or PA values. The odds ratio and the relative risk for active versus control were identical when PA and PP were used; however, the difference in proportion abstinent for active versus control was somewhat less when PA was used than when PP was used (8% vs. 10%). DISCUSSION: We conclude that PA and PP are closely related and can be interconverted with moderate accuracy. They also produce similar effect sizes when odds ratio and relative risk are used as effect sizes. When absolute difference in percent abstinent is used as an effect size, PA produces a smaller effect size than PP. We believe trials should continue to report both PA and PP outcomes to enhance comparisons across studies.