Construct Validity of IQ in the Presence of Scatter: A Measurement Invariance Approach

Practitioners of IQ tests are often taught that patterns of scatter among IQ subtests can lead to noncohesive full-scale IQ (FSIQ) scores. This notion exists despite a lack of empirical support and evidence for the robustness of FSIQ in the presence of scatter. However, to date, no study has directly tested the measurement invariance of groups varying in the amount of subtest scatter. We aimed to use multigroup confirmatory factor analysis to test the measurement invariance of the Stanford-Binet Intelligence Scales, fifth Edition (SB-5) for individuals with high vs. low scatter in a clinical sample of 5,352 individuals (ages 2-22) referred for comprehensive evaluations due to concerns for neurodevelopmental conditions. There was overall evidence for non-invariance in our sample, suggesting a limited impact of subtest scatter on the construct validity of IQ as measured by the SB-5. In addition, the explained variance of specific factors was low, even for individuals with high scatter among subtests. This study provides additional support for the robustness of FSIQ, even in cases of high scatter.