Comparison of cross-sectional and longitudinal designs in the study of aging of upper extremity performance

The purpose of the study was to compare two research designs, namely the cross-sectional design and the longitudinal design, in the context of upper extremity performance and age-related changes. Upper extremity performance of 360 randomly recruited, healthy, community-dwelling elderly persons was evaluated with reliable and valid sensorimotor tests. Three years later, survivors (n = 264) were reevaluated with the same tests. In many tests, cross-sectional and longitudinal design were comparable for estimating the changes in upper extremity performance with age. However, in some tests, the decline with age using a cross-sectional design was underestimated. The upper extremity performance decline observed with the longitudinal design was larger than the decline predicted with the cross-sectional design. The withdrawal and survivor biases related to the longitudinal design and the cohort bias associated with the cross-sectional design may, in part, explain these results.