F1 shows the least squares mean z score for each diagnostic group on each WISC subtest. After we controlled for gender, ethnicity, age at examination, handedness, and socioeconomic status, there was an overall main effect of diagnosis (F=9.50, df=2, 2051, p=0.0001) and a significant interaction of diagnosis and subtest (F=2.50, df=18, 2051, p=0.0004), indicating that the pattern of z scores across subtests differed among the diagnostic groups.
When we compared the subtest scores of the probands and normal comparison subjects, t tests (df=2051 for all) showed significant differences for the picture arrangement (t=–3.88, p=0.0001), vocabulary (t=–2.85, p=0.005), and coding (t=–6.08, p=0.0001) subtests but not for the block design (t=–0.95, p=0.34), information (t=–1.09, p=0.27), comprehension (t=–0.77, p=0.44), and digit span (t=–0.48, p=0.63) subtests. Similarly, the unaffected siblings performed significantly worse than the comparison subjects on the picture arrangement (t=–2.85, p=0.005), vocabulary (t=–2.90, p=0.004), and coding (t=–2.19, p=0.03) subtests but not on the block design (t=–0.91, p=0.36), information (t=–0.73, p=0.47), comprehension (t=–0.21, p=0.84), and digit span (t=–0.33, p=0.74) subtests. Finally, the probands performed significantly worse than their unaffected siblings only on the coding subtest (t=–2.64, p=0.009) and not on the block design (t=0.05, p=0.96), picture arrangement (t=–0.48, p=0.63), information (t=–0.20, p=0.84), comprehension (t=–0.39, p=0.70), vocabulary (t=0.30, p=0.76), and digit span (t=–0.08, p=0.94) subtests.