Normal variability of children's scaled scores on subtests of the Dutch Wechsler preschool and primary scale of intelligence-third edition

Intelligence tests are included in millions of assessments of children and adults each year (Watkins, Glutting, & Lei, 2007a, Applied Neuropsychology, 14, 13). Clinicians often interpret large amounts of subtest scatter, or large differences between the highest and lowest scaled subtest scores, on an intelligence test battery as an index for abnormality or cognitive impairment. The purpose of the present study is to characterize normal patterns of variability among subtests of the Dutch Wechsler Preschool and Primary Scale of Intelligence - Third Edition (WPPSI-III-NL; Wechsler, 2010). Therefore, the frequencies of WPPSI-III-NL scaled subtest scatter were reported for 1039 healthy children aged 4:0-7:11 years. Results indicated that large differences between highest and lowest scaled subtest scores (or subtest scatter) were common in this sample. Furthermore, degree of subtest scatter was related to: (a) the magnitude of the highest scaled subtest score, i.e., more scatter was seen in children with the highest WPPSI-III-NL scaled subtest scores, (b) Full Scale IQ (FSIQ) scores, i.e., higher FSIQ scores were associated with an increase in subtest scatter, and (c) sex differences, with boys showing a tendency to display more scatter than girls. In conclusion, viewing subtest scatter as an index for abnormality in WPPSI-III-NL scores is an oversimplification as this fails to recognize disparate subtest heterogeneity that occurs within a population of healthy children aged 4:0-7:11 years