Differential Item Functioning in the Wisc-III: Item Parameters for Boys and Girls in the National Standardization Sample

Abstract

The Wechsler Intelligence Scale for Children–Third Edition (WISC-III) is the most widely used test of intelligence in the world. However, the manual for the WISC-III provides insufficient detail regarding the detection of differential item functioning (DIF). The WISC-III national standardization sample ( N = 2,200) was used to investigate DIF in six WISC-III subtests. After fitting two parameter logistic and graded response models to the data, items were tested for DIF using the item response theory likelihood ratio DIF detection method. Of the 151 items studied, 52 were found to function differently across groups. The magnitude of the DIF was also considered by examining (a) parameter differences between groups and (b) root mean squared probability differences. Because the scores of boys and girls may be composed of different items systematically scored as correct, their IQs cannot be assumed to have the same meaning. Further investigations of item content bias are recommended.