Validity and item bias of the WISC-III with deaf children.

Abstract

The Wechsler Intelligence Scale for Children-Third Edition (WISC-III) is likely to become the most widely used test of intelligence with deaf children, based on the popularity of the previous versions of the test. Because the test was constructed for hearing children who use spoken English, the following major research questions were asked: (a) Does the WISC-III demonstrate adequate construct validity? and (b) Do specific items exhibit differential item functioning (DIF), and does the nature of the content of each item that exhibits DIF imply that the item is biased? The test was translated into sign language and administered to a total of 110 deaf children at three different sites. The deaf children ranged from ages 8 through 16 (M = 13.25, SD = 2.37), had hearing losses identified as severe or worse, were prelingually deaf, used sign language as their primary means of communication, and were not identified as having any additional handicapping conditions. The sample of deaf children was compared to a sample of 110 hearing children similar in age and Performance IQ. Construct validity was examined using a LISREL multi-sample covariance structure analysis. The covariance structures were different (χ ² (91) = 119.42, p =.024). A Rasch Model was used to detect DIF on the following subtests: Picture Completion, Information, Similarities, Arithmetic, Vocabulary, Comprehension. All of these subtests exhibited DIF, and DIF plus the differences in mean logit ability resulted in numerous items that were more difficult for deaf children on the above Verbal subtests. Item bias was judged by examining the contents of items that exhibited DIF. Items were biased due generally to translation issues and differences in the educational curricula. Thus, deaf children are at a distinct disadvantage when taking these WISC-III subtests. Practitioners are urged to consider these findings when assessing deaf children.