Table 1. Means, standard deviations and analysis of variance by sex and zygosity.
| ANOVA | |||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| All | MZ | DZ | Female | Male | Zyg. | Sex | Zyg.*Sex | Tot. | |||||||||
| Measures | M | SD | M | SD | M | SD | M | SD | M | SD | p | η² | p | η² | p | η² | R [Link] |
| Jigsaws total (0–28) | 16.82 | 3.47 | 16.71 | 3.40 | 16.88 | 3.51 | 16.66 | 3.38 | 16.92 | 3.52 | .337 | <.001 | .039 | .001 | .915 | <.001 | .002 |
| Hidden Shapes total (0–27) | 15.67 | 5.05 | 15.51 | 4.90 | 15.77 | 5.14 | 15.30 | 4.95 | 15.92 | 5.10 | .527 | <.001 | <.001 | .003 | .124 | .001 | .004 |
| Spatial Ability* | 0.00 | 0.82 | −0.04 | 0.80 | 0.02 | 0.84 | −0.06 | 0.80 | 0.04 | 0.84 | .220 | <.001 | <.001 | .003 | .431 | <.001 | .004 |
| Understanding Numbers (0–33) | 22.73 | 5.54 | 22.52 | 5.43 | 23.03 | 5.55 | 22.22 | 5.49 | 23.25 | 5.48 | .155 | <.001 | <.001 | .007 | .684 | <.001 | .009 |
| Non‐numerical Processes (0–25) | 15.98 | 4.77 | 15.88 | 4.71 | 16.13 | 4.88 | 15.71 | 4.79 | 16.25 | 4.83 | .522 | <.001 | .001 | .002 | .990 | <.001 | .003 |
| Computation & Knowledge (0–37) | 28.29 | 6.55 | 28.13 | 6.54 | 28.49 | 6.66 | 27.92 | 6.54 | 28.64 | 6.65 | .378 | <.001 | .001 | .002 | .444 | <.001 | .003 |
| Math total** | 0.02 | 0.89 | −0.04 | 0.86 | 0.05 | 0.90 | −0.08 | 0.86 | 0.08 | 0.90 | .112 | .001 | <.001 | .005 | .763 | <.001 | .008 |
*Spatial Ability is the mean of the two standardized spatial tests (requiring a score on both); **Math total is the mean of the three standardized mathematics tests (requiring a score on two out of the three subtests); ANOVA based on a random selection of one twin from each pair
ANOVA = analysis of variance; MZ = monozygotic; DZ = dizygotic; Zyg. = zygosity; Zyg.*Sex = zygosity by sex interaction term; Tot. = total variance explained by the ANOVA full model; M = mean; SD = standard deviation; p = p‐value; η² = partial eta squared; R2 = variance explained by zygosity, sex, and zygosity × sex interaction.