Test reliability and practice effects

The purpose of this paper is to develop mathematical formulations of test reliability when the estimation of reliability requires successive observations and these observations are not independent of the process (or act) of measurement. The specific application of concern arises in performance testing where performance varies as a function of practice and where practice accrues as a result of measurement. Repeated measures are experimentally nonindependent in such cases. Formulations for the estimation of reliability are developed for each of two cases. The first of these assumes a linear model for acquisition; the second assumes a nonlinear (quadratic) model. Illustrative data are presented whereby insights may be gained as to the inadequacy of the models.This investigation was supported by research grant (G14437) from National Science Foundation to Oregon Research Institute.The analysis of much of the data referred to in this report was made possible through the facilities of the Western Data Processing Center at the University of California, Los Angeles.