Table 1.
Means and variance components (and their 95% confidence intervals) of the educational achievement (EA) scores in 12-year-olds for each socioeconomic (SES) group as estimated in the genetic covariance structure models
| Lowest SES N = 891 twin pairs | Low SES N = 2889 twin pairs | High SES N = 2144 twin pairs | Highest SES N = 1005 twin pairs | |
|---|---|---|---|---|
| Means | ||||
| Girls | 533.2 (532.5–533.9) | 535.8 (535.4–536.1) | 538.9 (538.6–539.3) | 542.0 (541.4–542.5) |
| Boys | 534.5 (533.7–535.2) | 537.0 (536.7–537.4) | 540.1 (539.7–540.5) | 542.3 (541.8–542.9) |
| Unstandardized variances | ||||
| Phenotypic | 86.5 (80.0–93.7) | 79.1 (75.7–82.6) | 67.0 (63.8–70.5) | 59.0 (54.7–63.7) |
| Genetic | 65.9 (52.1–75.8) | 60.8 (53.7.–66.1) | 52.3 (46.6–56.1) | 47.8 (41.5–52.8) |
| Common environmental | 2.7 (0.0–15.8) | 1.8 (0.0–8.3) | 0.0 (0.0–4.9) | 0.0 (0.0–5.4) |
| Unique environmental | 17.9 (15.2–21.2) | 16.5 (15.0–18.1) | 14.7 (13.2–16.4) | 11.2 (9.6–13.2) |
| Proportion of phenotypic variance | ||||
| Genetic | 0.76 (0.60–0.83) | 0.77 (0.68–0.81) | 0.78 (0.70–0.80) | 0.81 (0.77–0.84) |
| Common environmental | 0.03 (0.00–0.18) | 0.02 (0.00–0.10) | 0.00 (0.00–0.07) | 0.00 (0.00–0.09) |
| Unique environmental | 0.21 (0.17–0.25) | 0.21 (0.19–0.23) | 0.22 (0.20–0.25) | 0.19 (0.16–0.23) |