Dealing with short-term fluctuation in longitudinal research.

OBJECTIVES Many analytical methods are not very sensitive to change because of the difficulty of distinguishing short-term fluctuation from the developmental change of primary interest. The current project investigated one possible solution to this problem in the form of a measurement-burst design in which research participants perform several versions of each test at each measurement occasion. METHODS Over 1,200 adults across a wide-age range performed different versions of cognitive tests on several sessions at each measurement occasion. RESULTS Four methods of incorporating short-term variability were compared with respect to the magnitude of the correlations of the ability measures with each other and with respect to the magnitude of their relations with age. CONCLUSIONS The results revealed that more sensitive assessments of change can be obtained by taking short-term fluctuation into account with measurement-burst designs. In particular, capitalizing on the availability of multiple measures at each occasion to form latent constructs representing the level and change in cognitive performance may provide the most sensitive assessment of cognitive change.