Identifying Test Items That Perform Differentially in Population Subgroups: A Partial Correlation Index

Abstract

Verbal items on the GRE Aptitude Test were analyzed for race (white vs. black) and sex differences in their functioning, using a new procedure—item partial correlations with subgroup standing (race or sex), controlling for total score—as well as two standard methods—comparisons of subgroups' item characteristic curves and item difficulties. The partial correlation index agreed with the item characteristic curve index in the proportions of items identified as performing differentially for each race and sex. These two indexes also agreed in the particular items that they identified as functioning differentially for the sexes, but not in the items that they identified as performing differently for the races. The partial correlation index consistently disagreed with the item difficulty index in the proportions of items identified as functioning differentially and in the particular items involved. The items identified by the partial correlation index as performing differentially, like the items identified by the other indexes, generally did not differ in type or content from items not so identified, with one major exception: this index identified items with female content as functioning differently for the sexes.