Cohort-Sequential Design

The cohort-sequential design — also called the accelerated longitudinal design — spans a long age range quickly by following several overlapping age cohorts for a short time each and then statistically linking their trajectory segments into one long developmental curve. Richard Bell introduced the idea in 1953 as 'convergence,' a way to study development over many years without waiting many years. Instead of following one cohort from, say, age 10 to age 20 for a full decade, the design enrolls cohorts aged 10, 12, 14, 16, and 18 and follows each for two or three years, with adjacent cohorts overlapping in age so their pieces can be joined. Yasuo Miyazaki and Stephen Raudenbush later supplied the formal multilevel tests for whether the cohorts can legitimately be linked. The design trades a single continuous within-person record for speed, while using overlap to check that the assembled curve is coherent.