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The purpose of this study is to investigate retest reliabilities in longitudinal study, the same test is administered repeatedly over time.Linear mixed models were used to establish various situations of tests occurred in longitudinal study.Combination of two types of true value and three types of systematic error was considered.In order to apply the models to real longitudinal data, height data from the Berkeley growth study and vocabulary score data from the University of Chicago experimental school were used.Using the mixed model, there is an advantage that the reliability can be determined by selecting the covariance structure of the true value and the error separately.However, in order to properly analyze the reliability, researchers need to consider variations that can occur in measurement, such as characteristics of subject, the test, and the the treatment applied in the study.And the proper model should be selected and the quality of the measurement should be evaluated for each trial.
Jinuk Kim (Wed,) studied this question.