Published online by Cambridge University Press: 01 January 2025
A logistic model developed by Birnbaum was tested in two ways. First, plots of proportions of subjects in different score categories were examined for consistency with the assumption of a logistic trace line, and especially for departures from the logistic which seemed due to guessing in multiple choice items. The results showed that guessing seemed to have little effect. Second, an attempt was made to predict the obtained score distributions of samples of subjects on six tests from item parameters estimated on independent samples. The fits were good in all cases, despite considerable differences between the tests, and some extremely odd distributions.
Thanks are due to the Educational Testing Service for the generous provision of the data upon which Part I of this study and the analysis of the two set I tests was based and to J. Lumsden for the data of the four set II tests. I would also like to thank F. M. Lord and A. Birnbaum for valuable help in the formulation and conduct of the study.
At the University of Michigan 1964–65.