Table 2.
Twin correlations and variance component estimates for task performance.
| Phenotypes | Twin correlations (95% CI) | Model fit: −2LL (Δχ2 (Δd.f.), p-value) | ACE estimates (%) full ACE model (95% CI) | ACE estimates (%) best fitting model (95% CI) | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| MZ | DZ | ACE | AE | CE | E | A | C | E | A | E | |
| 0-back | |||||||||||
| Accuracy (%) | 0.33* (0.13,0.50) | 0.08 (0.00,0.31) | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| RT (ms) | 0.54* (0.38,0.66) | 0.19 (0.00,0.42) | 3464.94 | 3464.94 (0.00 (1), ns) | 3471.29 (6.34 (1), <0.05) | 3497.69 (32.75 (2), <0.001) | 53 (14,66) | 0 (0,33) | 47 (34,63) | 53 (37,66) | 47 (34,63) |
| 2-back | |||||||||||
| Accuracy (%) | 0.55* (0.38,0.68) | 0.34* (0.12,0.53) | 2732.06 | 2732.42 (0.36 (1), ns) | 2734.96 (2.90 (1), ns) | 2765.43 (33.37 (2), <0.001) | 42 (0,68) | 13 (0,52) | 45 (32,62) | 57 (41,69) | 44 (31,59) |
| RT (ms) | 0.29* (0.11,0.44) | 0.20 (0.00,0.35) | 3895.92 | 3895.92 (0.00 (1), ns) | 3896.52 (0.60 (1), ns) | 3907.90 (11.98 (2), <0.01) | 34 (0,50) | 0.00 (0,34) | 66 (50,87) | 34 (15,50) | 66 (50,85) |
| FIQ | 0.77* (0.67,0.84) | 0.52* (0.32,0.66) | 2371.02 | 2373.00 (1.98 (1), ns) | 2380.60 (9.58 (1), <0.01) | 2455.34 (84.32 (2), <0.001) | 50 (18,82) | 27 (0,56) | 23 (16,33) | 78 (68,84) | 22 (16,32) |
Maximum likelihood twin correlations, univariate genetic model fitting results and variance component estimates from the full ACE and best fitting models for the performance measures and FIQ. Best fitting model is underlined. Nested sub-models are compared to the full ACE model by testing whether dropping a parameter resulted in a significant increase in the goodness-of-fit chi-squared (the difference in minus 2 times the log likelihood (−2LL) of a model and a nested submodel follows a chi-square distribution with degrees of freedom equal to the difference in the number of parameters). Estimates are corrected for age and sex; assumption testing supported homogeneity of means and variances across birth order and zygosity. Abbreviations: −2LL = minus 2*log-likelihood; Δχ2 = change in chi-square; Δd.f. = change in degrees of freedom; CI, confidence interval; FIQ, Full-scale Intelligence Quotient; ms, milliseconds; ns, not significant; RT, Reaction Time.