Table 1.
Descriptive statistics and phenotypic correlations
| Age 4 years | Age 7 years | Age 9 yearsa | Age 16 years | |
|---|---|---|---|---|
| Sample size, n | ||||
| MZ | 5072 | 5202 | 2421 | 3497 |
| DZ | 9671 | 9216 | 4103 | 6150 |
| Total | 14 743 | 14 418 | 6524 | 9647 |
| Descriptive statistics | ||||
| Mean age, years (s.d.) | 4.04 (0.13) | 7.07 (0.25) | 9.02 (0.29) | 16.32 (0.68) |
| Cronbach’s α for OCB scale | 0.59 | 0.59 | 0.62 | 0.61 |
| Mean OCB score (s.d.) | 2.56 (1.75) | 1.89 (1.56) | 0.94 (1.13) | 0.82 (1.26) |
| Phenotypic correlations | ||||
| Age 4 years | ||||
| r | 1 | |||
| n | 14 743 | |||
| Age 7 years | ||||
| r (95% CI) | 0.45 (0.43–0.46) | 1 | ||
| n | 11 276 | 14 418 | ||
| Age 9 years | ||||
| r (95% CI) | 0.35 (0.32–0.37) | 0.44 (0.42–0.46) | 1 | |
| n | 5409 | 5771 | 6524 | |
| Age 16 years | ||||
| r (95% CI) | 0.23 (0.21–0.26) | 0.32 (0.30–0.34) | 0.37 (0.34–0.40) | 1 |
| n | 7891 | 8053 | 4054 | 9647 |
MZ, Monozygotic; DZ, dizygotic; s.d., standard deviation; OCB, obsessive–compulsive behaviour; CI, confidence interval.
a
At age 9 years, the study was restricted to just two out of three cohorts, resulting in a reduced sample size.