期刊名称：International Journal of Educational Methodology
电子版ISSN：2469-9632
出版年度：2020
卷号：6
期号：2
页码：297-317
DOI：10.12973/ijem.6.2.297
出版社：Tayfun Yagar
摘要：A new index of item discrimination power (IDP), dimension-corrected Somers’ D (D2) is proposed. Somers’ D is one of the
superior alternatives for item–total- (Rit) and item–rest correlation (Rir) in reflecting the real IDP with items with scales 0/1 and
0/1/2, that is, up to three categories. D also reaches the extreme value +1 and ‒1 correctly while Rit and Rir cannot reach the
ultimate values in the real-life testing settings. However, when the item has four categories or more, Somers’ D underestimates IDP
more than Pearson correlation. A simple correction to Somers’ D in the polytomous case seems to lead to be effective in item analysis
settings. In the simulation with real-life items, D2 showed very few cases of obvious underestimation and practically no cases of
obvious overestimation. With certain restrictions discussed in the article, D2 seems to be a good alternative for these classic
estimators not only with dichotomous items but also with the polytomous ones. In general, the magnitudes of the estimates by D2
are higher than those by Rit, Rir, and polychoric correlation and they seem to be close of those of bi- and polyserial correlation
coefficients without out-of-range values.
