N Rotation/Visualisation Visualisation 2D 3D Overall Bricks 0.33 (0.26?.41) 0.38 (0.31?.46) 0.45 (0.38?.51) 0.47 (0.40?.53) 0.41 (0.33?.48) 0.56 (0.49?.61) DZ 0.21 (0.14?.28) 0.22 (0.14?.28) 0.22 (0.15?.29) 0.25 (0.18?.31) 0.20 (0.13?.27) 0.27 (0.20?.33) Variance component estimates h2 0.25 0.34 0.45 0.44 0.41 0.56 c2 0.09 0.05 0.00 0.02 0.00 0.00 e2 0.67 0.62 0.55 0.53 0.59 0.44 Sample (numbers of pairs) MZ 520 521 516 526 508 522 DZ 714 714 711 724 697Table 1. Twin correlations and approximated variance components. Intraclass twin correlations (95 confidence intervals) for MZ and DZ twins, for the Bricks composites. Variance component estimates are heritability (h2: double the difference between the MZ and DZ correlations, constrained not to exceed the former Z twins are genetically identical, so heritability cannot exceed their correlation), shared environment (c2: the MZ correlation minus h2), and EPZ004777 site unique environment + error of measurement (e2: 1-h2-c2). Sample sizes shown are complete pairs, after exclusions and data cleaning. However, it must be noted that the subtests were not intended for use in this way, being very short individually in comparison to most cognitive tests nd thus not very highly reliable n order to keep the administration of the whole battery within a reasonable time limit. The results from the individual subtests should therefore be treated with caution, and the Bricks composites were created on the original theoretical grounds, to assess whether clearer distinctions might emerge from the more reliable constructs. The resulting functional composites were moderately intercorrelated. If mental rotation and spatial visualisation are functionally distinct, we would predict the Rotation and Visualisation composites to be correlated more modestly with each other than either is with Rotation/Visualisation combined. In fact, the results showed that the TAPI-2 biological activity association between Rotation and Visualisation (r = 0.46, p < 0.0001, N = 1411) was identical to that between Rotation and Rotation/Visualisation combined (r = 0.46, p < 0.0001, N = 1423), and the correlation between Visualisation and Rotation/Visualisation combined (r = 0.54, p < 0.0001, N = 1426; the slight variations in sample size result from losses during data cleaning, described in the Supplementary Methods online) did not differ substantially (although the small difference was significant in this large sample; p < 0.001). However, these correlations are far from unity, as is that between the 2D and 3D composites (r = 0.56, p < 0.0001, N = 1413), which suggests some specificity between the composites. The nature of this specificity is the subject of the multivariate genetic analyses below. The Bricks composites correlated modestly with verbal ability (average r = 0.20), and moderately with non-verbal ability (r = 0.43) and g (r = 0.38); see Supplementary Table S5. It was considered that the associations among the Bricks scores could be driven in part by more domain-general abilities or processes captured by these other measures, which could potentially obscure the "true" relationships among the Bricks subtests and composites. Accordingly, the Bricks subtests and composites were regressed separately on verbal ability (a conservative under-correction for domain-general processes; see Methods), on non-verbal ability (perhaps an over-correction including some of the variance in spatial ability, reflected in its higher correlations with Bricks), and on g (their mean). T.N Rotation/Visualisation Visualisation 2D 3D Overall Bricks 0.33 (0.26?.41) 0.38 (0.31?.46) 0.45 (0.38?.51) 0.47 (0.40?.53) 0.41 (0.33?.48) 0.56 (0.49?.61) DZ 0.21 (0.14?.28) 0.22 (0.14?.28) 0.22 (0.15?.29) 0.25 (0.18?.31) 0.20 (0.13?.27) 0.27 (0.20?.33) Variance component estimates h2 0.25 0.34 0.45 0.44 0.41 0.56 c2 0.09 0.05 0.00 0.02 0.00 0.00 e2 0.67 0.62 0.55 0.53 0.59 0.44 Sample (numbers of pairs) MZ 520 521 516 526 508 522 DZ 714 714 711 724 697Table 1. Twin correlations and approximated variance components. Intraclass twin correlations (95 confidence intervals) for MZ and DZ twins, for the Bricks composites. Variance component estimates are heritability (h2: double the difference between the MZ and DZ correlations, constrained not to exceed the former Z twins are genetically identical, so heritability cannot exceed their correlation), shared environment (c2: the MZ correlation minus h2), and unique environment + error of measurement (e2: 1-h2-c2). Sample sizes shown are complete pairs, after exclusions and data cleaning. However, it must be noted that the subtests were not intended for use in this way, being very short individually in comparison to most cognitive tests nd thus not very highly reliable n order to keep the administration of the whole battery within a reasonable time limit. The results from the individual subtests should therefore be treated with caution, and the Bricks composites were created on the original theoretical grounds, to assess whether clearer distinctions might emerge from the more reliable constructs. The resulting functional composites were moderately intercorrelated. If mental rotation and spatial visualisation are functionally distinct, we would predict the Rotation and Visualisation composites to be correlated more modestly with each other than either is with Rotation/Visualisation combined. In fact, the results showed that the association between Rotation and Visualisation (r = 0.46, p < 0.0001, N = 1411) was identical to that between Rotation and Rotation/Visualisation combined (r = 0.46, p < 0.0001, N = 1423), and the correlation between Visualisation and Rotation/Visualisation combined (r = 0.54, p < 0.0001, N = 1426; the slight variations in sample size result from losses during data cleaning, described in the Supplementary Methods online) did not differ substantially (although the small difference was significant in this large sample; p < 0.001). However, these correlations are far from unity, as is that between the 2D and 3D composites (r = 0.56, p < 0.0001, N = 1413), which suggests some specificity between the composites. The nature of this specificity is the subject of the multivariate genetic analyses below. The Bricks composites correlated modestly with verbal ability (average r = 0.20), and moderately with non-verbal ability (r = 0.43) and g (r = 0.38); see Supplementary Table S5. It was considered that the associations among the Bricks scores could be driven in part by more domain-general abilities or processes captured by these other measures, which could potentially obscure the "true" relationships among the Bricks subtests and composites. Accordingly, the Bricks subtests and composites were regressed separately on verbal ability (a conservative under-correction for domain-general processes; see Methods), on non-verbal ability (perhaps an over-correction including some of the variance in spatial ability, reflected in its higher correlations with Bricks), and on g (their mean). T.