Classical methods for detecting outliers deal with continuous variables. These methods are not readily applicable to categorical data, such as incorrect/correct scores (0/1) and ordered rating scale scores (e.g., 0,..., 4) typical of multi-item tests and questionnaires. This study proposes two definitions of outlier scores suited for categorical…

Three computer simulations were conducted to show that very high aggregate predictive validity coefficients can occur when the across-case variability in absolute score stability occurring in both the predictor and criterion matrices is quite small. In light of the increase in internal consistency reliability achieved by the method of aggregation…

This commentary focuses on the application of D. Rogosa and G. Ghandour's work to observational research on classroom processes. Rogosa and Ghandour have shown that the short length of an observation is typically the dominant source of error. Investigators should conduct observations for as long as possible. (SLD)

This manual is intended to improve both the design of longitudinal studies and analysis of the resulting data. Issues related to educational and developmental research have been emphasized in these eight chapters. Topics of particular interest to longitudinal researchers include stochastic models of developmental change, mathematical…