Table 6.
Multiple regression analysis between the University Selection Test (PSU) (mean language + mathematics), language PSU and mathematics PSU scores (dependent variables) and the most relevant parameters (independent variables).
| Parameter | Estimate | Standard Error of Estimate |
T for H0: Parameter = 0 |
p >|T| |
|---|---|---|---|---|
| PSU score (mean language + mathematics) | ||||
| Intercept | −291.5 | 139.4 | −2.09 | .0393 |
| IA (Ref: Grades IV + V) | ||||
| Grade I + II | 239.3 | 26.9 | 8.87 | .0001 |
| Grade III | 49.8 | 26.0 | 1.92 | .0586 |
| GMV | 0.59 | 0.15 | 3.90 | .0002 |
| rIFG | 106.9 | 37.4 | 2.86 | .0053 |
| SES (Ref: Medium) | ||||
| High SES | 16.6 | 20.1 | 0.83 | .4097 |
| Low SES | 44.6 | 18.4 | 2.41 | .0178 |
| Sex (Ref: males) | ||||
| Females | −27.8 | 19.1 | 1.45 | .1505 |
| Language PSU score | ||||
| Intercept | −251.3 | 148.0 | −1.70 | .0930 |
| IA (Ref: Grades IV + V) | ||||
| Grade I + II | 235.9 | 28.6 | 8.24 | .0001 |
| Grade III | 68.7 | 27.6 | 2.49 | .0146 |
| GMV | 0.64 | 0.16 | 4.03 | .0001 |
| SES (Ref: Medium) | ||||
| High SES | 26.9 | 21.3 | 1.26 | .2113 |
| Low SES | −41.5 | 19.6 | −2.12 | .0368 |
| rIFG | 71.0 | 39.7 | 1.79 | .0770 |
| Sex (Ref: males) | ||||
| Females | −35.8 | 20.3 | 1.76 | .0817 |
| Mathematics PSU score | ||||
| Intercept | −321.8 | 175.5 | −1.83 | .0699 |
| IA (Ref: Grades IV + V) | ||||
| Grade I + II | 238.8 | 32.8 | 7.27 | .0001 |
| Grade III | 27.5 | 32.0 | 0.86 | .3912 |
| rIFG | 142.9 | 47.5 | 3.00 | .0034 |
| GMV | 0.52 | 0.19 | 2.75 | .0071 |
| SES (Ref: Medium) | ||||
| High SES | 6.08 | 25.5 | 0.24 | .8127 |
| Low SES | −49.1 | 23.2 | −2.12 | .0370 |
| Sex (Ref: males) | ||||
| Females | −18.3 | 24.1 | 0.76 | .4494 |
Model R2 = .811; Root MSE (Root mean squared error, standard deviation of the dependent variable PSU) = 71.4949; Model F Value = 55.76, p < .0001.
Model R2 = .770; Root MSE (Root mean squared error, standard deviation of the dependent variable language PSU) = 75.9123; Model F Value = 43.61, p < .0001.
Model R2 = .750; Root MSE (Root mean squared error, standard deviation of the dependent variable mathematics PSU) = 90.9008; Model F Value = 39.52, p < .0001.
IA, intellectual ability; IA grades: Grade I, superior; Grade II, above average; Grade III, average; Grade IV, below average; Grade V, intellectually defective. GMV, gray matter volume. rIFG, right inferior frontal gyrus thickness. SES, socio-economic status. The initial regressors (independent variables considered in the statistical model) considered for the forward stepwise selection method were IA, SES, sex, brain segmentation without ventricles, GMV, brainstem, rIFG, right cerebellum cortex, left cerebellum cortex.