A reanalysis of gender differences in IQ scores following unilateral brain lesions

Meta-analyses of gender differences in the consequences of unilateral brain lesions have reported a positive correlation between the percentage of men in studies and the magnitude of the difference between Verbal and Performance IQ. Such findings are limited by both the indirectness of the methodology and the focus on V-P differences rather than on the separate effects of brain lesions on VIQ and PIQ. We conducted a repeated-measures analysis of studies that reported separate VIQ and PIQ means for men and women with unilateral lesions. Women showed lower IQ scores following lesions to the hemisphere thought to be nondominant for each function. Gender differences in the effects of unilateral brain lesions on intellectual performance have been observed for more than 25 years (Lansdell, 1962). Male patients appear to experience greater lateralized intellectual deficits following unilateral lesions, as measured by greater discrepancies between Verbal and Performance IQ scores. Such a gender difference is potentially important because of its implications for fundamental questions of functional brain organization in men and women, and because differences between VIQ and PIQ have been used as psychometric signs of lateralized brain damage (e.g., Lawson & Inglis, 1983). This gender difference has received renewed attention since Inglis and Lawson (1981,1982) reported a correlation of 0.48 between Verbal-Performance (V-P) discrepancy and the percentage of men included in 18 samples from 16 different studies. Inglis and Lawson's meta-analysis was replicated, using additional samples, by Bornstein and Matarazzo (1982), Bornstein (1984), and Snow, Freedman, and Ford (1986). The unusual meta-analytic methodology of correlating V-P discrepancies with the percentage of male subjects in each study was necessitated by the paucity of studies reporting Verbal and Performance IQs separately for male and female subjects. More recently, Kaufman (1990) identified a sample of eight studies that reported V-P discrepancies separately for male and female subjects. In patients with right hemisphere lesions, V-P differences were twice as large in male as in female subjects. In male patients with left hemisphere lesions, mean PIQ was higher than the mean VIQ, whereas in female patients with left hemisphere lesions the mean PIQ was slightly higher. We believe another brief examination of this literature is warranted. There are now 12 studies that have reported eight separate means for Verbal and Performance IQ in male and female patients with left and right hemisphere lesions. Analysis of these studies will allow gender differences to be studied with greater precision than was possible with the useful but indirect