Aspects of statistical design for the Community Intervention Trial for Smoking Cessation (COMMIT)

We present statistical considerations for the design of the Community Intervention Trial for Smoking Cessation (COMMIT). One outcome measurement, the quit rate in randomly selected cohorts of smokers, is compared with another outcome measurement, the decrease in smoking prevalence, in terms of statistical efficiency and interpretability. The COMMIT study uses both types of outcome measurements. The merits of pair-matching the communities are considered, and sample size calculations take into account heterogeneity among pair-matched communities. In addition to significance tests based on the permutational (randomization) distribution, we also describe approaches for covariate adjustment. The COMMIT design includes 11 pair-matched communities, which should provide good power to detect a 10% or greater difference in quit rates between the intervention and control communities in cohorts of heavy smokers and in cohorts of light or moderate smokers. The power is only moderate to detect intervention effects on the decreases in overall smoking prevalence or in the prevalence of heavy smoking.