Results of this study indicate that the correlation between half-test scores over repeated splits, over persons, and over repeated testings resulting in different sets of observed scores, is given by Kuder-Richardson Formula 21. (RF)

Although a great deal of attention has been devoted over a period of years to the estimation of reliability from item statistics, there are still gaps in the mathematical derivation of the Kuder-Richardson results. The main purpose of this paper is to fill some of these gaps, using language consistent with modern probability theory. (Author)

Using the concepts of conditional probability, conditional expectation, and conditional independence, the main results of the classical test theory model can be derived in a very few steps with minimal assumptions. The present effort explores the possibility that present classical test theories can be further condensed. (Author/RC)