William H. Angoff

The Evaluation of Differences in Test Performance of Two or More Groups

A two-factor analysis of variance with multiple measurements on one factor was conducted among the 40 items of the Vocabulary test of TOEFL for six language groups. All sources of variance were found to be significant beyond the one per cent level. Of particular interest was the item x group interaction which was examined by analyzing the item difficulty plots for each language group against a spaced sample of all candidates taking this form of the test at its first formal administration. A measure of the deviation of each item from the central tendency of the plot was developed, expressing the degree to which the item was especially difficult or especially easy for a particular language group relative to the other items. A distribution of these measures is given for each of the six language groups.

A note on the estimation of nonspurious correlations

A method is provided for estimating the nonspurious correlation of a part of a test with the total test. Two cases are considered: one in which the actual subtest is parallel to the total test, the other in which the actual subtest is not parallel to the total test.