Table 2.
Descriptive statistics for NSSH and SSH
| Phenotype | Frequency | Full sample | Male | Female | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Total N | N | % | Total N | N | % | Total N | N | % | ||
| NSSH | No | 9063 | 7080 | 78.1 | 3407 | 2887 | 84.7 | 5656 | 4193 | 74.1 |
| Yes, once or twice | 951 | 10.5 | 295 | 8.7 | 656 | 11.6 | ||||
| Yes, 3–5 times | 293 | 3.2 | 72 | 2.1 | 221 | 3.9 | ||||
| Yes, 6–10 times | 195 | 2.2 | 39 | 1.1 | 156 | 2.8 | ||||
| Yes, more than 10 times | 544 | 6.0 | 114 | 3.3 | 430 | 7.6 | ||||
| SSH | No | 9061 | 8106 | 89.5 | 3407 | 3143 | 92.3 | 5654 | 4963 | 87.8 |
| Yes, once or twice | 640 | 7.1 | 180 | 5.3 | 460 | 8.1 | ||||
| Yes, 3–5 times | 144 | 1.6 | 47 | 1.4 | 97 | 1.7 | ||||
| Yes, 6–10 times | 60 | 0.7 | 11 | 0.3 | 49 | 0.9 | ||||
| Yes, more than 10 times | 111 | 1.2 | 26 | 0.8 | 85 | 1.5 | ||||
| Mean age (years) | 22.3 | 22.3 | 22.2 | |||||||
| Number of twins reporting ‘Yes’ for either NSSH or SSH, or both (%) | 2057 (22.7%) | 542 (15.9%) | 1515 (26.8%) | |||||||
| Number of twins reporting ‘Yes’ for both NSSH and SSH (%) | 881 (9.7%) | 242 (7.1%) | 639 (11.3%) | |||||||
| Number of twins reporting ‘Yes’ for NSSH only (%) | 1102 (12.2%) | 278 (8.2%) | 824 (14.6%) | |||||||
| Number of twins reporting ‘Yes’ for SSH only (%) | 74 (0.8%) | 22 (0.6%) | 52 (0.9%) | |||||||