Using McCarthy scales extrapolated general cognitive indexes below 50: some words of caution.

Abstract

An often cited criticism of the McCarthy Scales of Children's Abilities is that the General Cognitive Index is of limited use for gifted and retarded children because of its inadequate ceiling and floor ( 2 ) . Harrison and Naglieri ( 1 ) presented tables of General Cognitive Indexes for use with such groups, raising the ceiling from 150 to 172, and lowering the floor from 50 to 28. As they stated, extrapolated values are useful for estimating a child's present level of functioning; however, because values are not based on empirical data, they should be viewed as estimates and used with caution (p. 1291). Levenson and Zino ( 3 ) tested matched samples of retarded and normal youngsters with both the Stanford-Binet and McCarthv scales. Correlational analvses and their interpretation were hindered in that General Cognitive Indexes of below 50 were found for the majority of subjects. To facilitate the analysis, correlations were computed between McCarthy composite raw scores and Binet IQs. The present study utilized General Cognitive Indexes to determine the relationship between the McCarthy scales and Stanford-Binet for assessing the level of functioning of retarded children. Data for the study were taken from Levenson and Zino ( 3 ) for 15 retarded children (seven boys, eight girls, with a mean age of 6-6) . A comparison of means for StanfordBinec IQs ( M = 64.46. SD = 12.73; Mdn = 66.0) and McCarthy scales General Cognitive Indexes ( M = 44.26, SD = 21.45; Mdn = 37.0) was significant ( t = 3.02, 28 d f , f i < 0.01). Factors affecting the significance of differences between means may have been the error rate associated with scores, and the absence of empirical data on retarded subjects from the standardization sample of the McCarthy scales. Therefore, while General Cognitive Indexes below 50 may aid psychologists in approximating cognitive ability levels, data for these 15 children indicate that the Indexes should only be used with extreme caution.