Comparison of McCarthy General Cognitive Index and Wisc-R IQ for Educable Mentally Retarded, Learning Disabled, and Normal Children

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Abstract
The relationship between the McCarthy General Cognitive Index and the WISC-R Full Scale IQ was examined for 20 educable mentally retarded, 20 learning disabled, and 20 normal children aged 6 to 8½ yr. Selection of children was conducted so that the three groups would be comparable with res pea to age, sex, and race. The mean McCarthy Indexes for the retarded and learning disabled samples were significantly lower than the mean WISC-R Full Scale IQs. When the Index and Full Scale IQ were converted to a common metric and compared, the mean index for the retarded and learning disabled samples remained lower than the Full Scale IQs, although the differences were nonsignificant. The measures correlated significantly for all three samples and ranged from .51 to .82.