Table 2 Twin-to-singleton ORs in the different levels of the categorial moderator variables within the non-right-handedness (NRH) comparison. Overall, 20 studies were included in the NRH comparison (see main text).
Variable | Levels | Studies (k) | Participants (n) | Twins | Singletons | twin-to-singleton NRH OR [95% CI] |
|---|---|---|---|---|---|---|
Sicotte et al. [10] meta-analysis | Yes (included in Sicotte et al. [10]) | 13 | 85,371 | 8281 | 77,090 | 1.43 [1.23, 1.66] |
| Â | No (new study) | 6 | 38,394 | 30,773 | 7621 | 1.26 [1.01, 1.57] |
Ancestry | Europe/USA/Australia | 16 | 101,828 | 38,090 | 63,738 | 1.40 [1.23, 1.59] |
| Â | East Asia | 3 | 21,937 | 964 | 20,973 | 1.16 [0.79, 1.72] |
Study purpose | Handedness in twins | 17 | 187,645 | 49,375 | 138,270 | 1.38 [1.23, 1.54] |
| Â | Other purpose | 3 | 1629 | 691 | 938 | 1.21 [0.85, 1.74] |
Type of singleton group | Genetically related to the twins | 4 | 77,763 | 15,614 | 62,149 | 1.31 [1.07, 1.60] |
| Â | Genetically unrelated to the twins | 12 | 103,122 | 33,799 | 69,323 | 1.41 [1.22, 1.63] |
Handedness classification | R-A-L | 4 | 38,975 | 26,511 | 12,464 | 1.12 [0.87, 1.45] |
| Â | R-L | 12 | 83,177 | 11,852 | 71,325 | 1.45 [1.26, 1.68] |
Method of handedness assessment | Preference obtained from inventories containing more than one item | 5 | 16,721 | 1560 | 15,161 | 1.57 [1.26, 1.95] |
| Â | Self-reports/writing hand | 12 | 170,689 | 47,700 | 122,989 | 1.32 [1.19, 1.47] |