Table II.
Group means and variances
| Mean | Variance | P value | ||||
|---|---|---|---|---|---|---|
| MZ | DZ | MZ | DZ | Mean | Variance | |
| ICV | 460.11 | 465.99 | 3889.01 | 3674.23 | 0.6390 | 0.8415 |
| Lateral ventricles | 4.35 | 4.64 | 2.21 | 4.25 | 0.3984 | 0.0113 |
| Total GM | 233.07 | 238.81 | 987.89 | 917.21 | 0.3623 | 0.7913 |
| Total WM | 156.59 | 160.86 | 433.45 | 525.33 | 0.3375 | 0.4884 |
| Total EM | 10.64 | 10.30 | 13.98 | 12.94 | 0.5740 | 0.7312 |
| Total CSF | 59.80 | 56.09 | 180.02 | 151.33 | 0.1435 | 0.5023 |
| Cortical GM | 193.93 | 198.04 | 692.46 | 610.95 | 0.4310 | 0.6547 |
| Cortical WM | 148.68 | 153.16 | 368.11 | 466.73 | 0.2774 | 0.3897 |
| SubCortGM | 15.90 | 16.08 | 8.69 | 7.87 | 0.7345 | 0.6929 |
| Cerebellum | 23.21 | 24.68 | 17.62 | 21.75 | 0.1076 | 0.4511 |
| Prefrontal GM | 26.48 | 26.73 | 27.09 | 22.61 | 0.7988 | 0.4925 |
| Frontal GM | 42.03 | 43.35 | 36.35 | 34.01 | 0.2655 | 0.8034 |
| Parietal GM | 57.98 | 59.93 | 65.55 | 52.81 | 0.2031 | 0.4166 |
| Occipital GM | 67.60 | 68.12 | 111.53 | 96.33 | 0.8065 | 0.5839 |
| Prefrontal WM | 24.18 | 24.37 | 13.41 | 16.11 | 0.8097 | 0.5014 |
| Frontal WM | 37.03 | 37.61 | 23.00 | 27.27 | 0.5552 | 0.5230 |
| Parietal WM | 45.78 | 48.24 | 41.88 | 53.47 | 0.0769 | 0.3652 |
| Occipital WM | 40.09 | 41.50 | 39.71 | 49.31 | 0.2876 | 0.4215 |
| Total prefrontal | 51.48 | 51.76 | 76.76 | 68.63 | 0.8625 | 0.6801 |
| Total frontal | 80.74 | 82.31 | 108.72 | 111.29 | 0.4543 | 0.9203 |
| Total parietal | 105.99 | 110.53 | 202.47 | 208.70 | 0.1160 | 0.8875 |
| Total Occipital | 110.16 | 112.07 | 276.17 | 265.72 | 0.5657 | 0.8875 |
| RHem GM | 99.16 | 101.37 | 189.04 | 166.31 | 0.4131 | 0.6468 |
| LHem GM | 94.79 | 96.68 | 161.41 | 143.51 | 0.4503 | 0.6714 |
| RHem WM | 71.44 | 73.88 | 87.67 | 109.89 | 0.2253 | 0.4131 |
| LHem WM | 75.61 | 77.77 | 95.09 | 124.18 | 0.3055 | 0.3323 |
| RHem Tot | 174.06 | 178.56 | 522.00 | 520.18 | 0.3323 | 1.0000 |
| LHem Tot | 174.17 | 177.99 | 501.24 | 510.88 | 0.4028 | 0.9203 |
| Corpus callosum | 1.75 | 1.56 | 0.25 | 0.13 | 0.0288 | 0.0131 |
Abbreviations: CSF, cerebrospinal fluid; EM, early myelinated white matter; GM, gray matter; ICV, intracranial volume; LHem, left hemisphere; RHem, right hemisphere; SubCortGM, subcortical gray matter; WM, unmyelinated white matter.