The previous theoretical development of the Poisson process as a strong model for the true-score theory of mental tests is discussed, and additional theoretical properties of the model from the standpoint of individual examinees are developed. The paper introduces the Erlang process as a family of test theory models and shows in the context of…

The equivalency of achievement results obtained under Title I evaluation models A1 and C1 was examined. Data were reading comprehension and arithmetic scores on the Iowa Tests of Basic Skills, administered to fourth, sixth, and eighth grade students in St. Louis, Missouri. The St. Louis Public Schools had traditionally used Model A1, a…