Comparative dental caries activity in dropouts and non-dropouts from a three-year study.

Design of a clinical study to determine the impact of an experimental agent or regimen on dental caries activity must balance a number of interacting variables to yield meaningful results. At the outset, caries experience must be determined for each subject to permit sample stratification that will, in addition to age and sex, divide dental caries risk equally between the experimental groups. Unfortunately, some individuals discontinue participation during the course of the study. How damaging this will be to group caries risk equality depends on several factors, some obvious and others inapparent. For example, a correlation might exist between those habits or attitudes that are expressed overtly in discontinuance of participation and the measure under examination-dental caries activity. Could it be that dropouts have a peculiar or unusual dental caries rate or risk, and, by withdrawing unequally from experimental groups, do they destroy otherwise legitimate sample comparability? This study examines comparability of dental caries experience during a one-year period in two study samples; one group subsequently discontinued participation and the other completed all three years of the study.