A model for the study of development processes in dental research.

In studying growth and developmental processes in dental research, variables other than simple chronological age must often be taken into account if we are to adequately characterize differences in the developmental patterns of the groups under consideration. As demonstrated in this article, cohort, time-of-measurement, and learning (testing) effects may significantly interfere with our ability to directly study development if the traditional cross-sectional and longitudinal designs are used. Mixed-longitudinal studies, with well-scheduled control groups, may better serve the dental research community in the design of studies dealing with the measurement of change.