Error of Measurement in Longitudinal Designs: Defining, Identifying, and Correcting for Specific Error and Transient Error1

This manuscript addresses errors of measurement that exist in cross-sectional research, but that are not readily recognized unless longitudinal data are collected. Both specific and transient errors of measurement are defined, a method of identifying them if they exist is presented, a method of correcting for them is presented, and their implications for longitudinal data analysis are briefly discussed.