No statistically significant differences in area between the groups were found for the best midsagittal slice (F=1.03, df=2, 48, p=0.54), average of five slices (F=1.92, df=2, 48, p=0.18), or subdivisions of the genu (F=0.14, df=2, 48, p=0.72), midbody (F=1.24, df=2, 48, p=0.29), isthmus (F=1.17, df=2, 48, p=0.30), or splenium (F=0.20, df=2, 48, p=0.66). Using ANCOVA to control for the effects of age and size of the intracranial cavity, we found no significant differences in area between groups. As there are gender differences in corpus callosum size (7), we excluded 10 female subjects in one analysis; there were no area differences between the schizophrenia and comparison groups (F=0.26, df=1, 25, p=0.61) or between the affective disorder and comparison groups (F<0.01, df=1, 28, p=0.96). For all groups, there were no statistically significant correlations between area and lateral ventricular volumes, nor between area and MMSE, BPRS, or GAS scores or chlorpromazine equivalents of medication received by the subjects.
For analysis of shape, an angles-and-widths multinomial regression model was used (on the basis of the eight equidistant points used to extract the skeleton image) to obtain the classification data for examining each of three two-by-two classification tables. The three two-by-two contrasts (comparison versus affective disorder, comparison versus schizophrenia, and affective disorder versus schizophrenia) were estimated by bootstrap methods, with chi-square statistics (df=16) defined as the mean chi square among all 100 bootstrap repetitions. The contrast between the comparison and schizophrenia groups was statistically significant (χ2=30.6, df=16, p<0.02). The other contrasts were not statistically significant (comparison versus affective disorder: χ2=19.3, df=16, p=0.25; affective disorder versus schizophrenia: χ2=20.3, df=16, p=0.21). The lower part of F1 shows prototypic corpus callosum shapes for each diagnostic group.
For shape measures, there were no statistically significant correlations of average angle and width with area, lateral ventricular volumes, or scores on the clinical measures (MMSE, BPRS, GAS). In the affective disorder group only, as the width decreased, the angle decreased (r=0.89, df=18, p<0.02), i.e., as the corpus callosum width narrowed, the shape became more curved.