an experimental design in which multiple measures are taken over a period of time from two or more groups of different ages (birth cohorts). If, for instance, individuals ranging in age from 5 to 10 years are sampled and then the members of each age group are studied for a 5-year period, the resulting data would span 15 years of development. Such studies essentially are a combination of a longitudinal design and a cross-sectional design. Also called accelerated longitudinal design.