Table 2.

Proportion of phenotypic variance and covariance accounted for by A, C and E^a

	Age 4 years	Age 7 years	Age 9 years	Age 16 years
Proportion of phenotypic variance and covariance accounted for by A
Age 4 years	0.59 (0.57–0.61)
Age 7 years	0.75 (0.70–0.79)	0.61 (0.57–0.63)
Age 9 years	0.80 (0.70–0.91)	0.70 (0.66–0.86)	0.54 (0.46–0.61)
Age 16 years	0.78 (0.68–0.97)	0.59 (0.43–0.75)	0.72 (0.57–1.00)	0.33 (0.26–0.41)
Proportion of phenotypic variance and covariance accounted for by C
Age 4 years	0.00 (0.00–0.01)
Age 7 years	0.01 (0.00–0.04)	0.02 (0.01–0.04)
Age 9 years	0.00 (0.00–0.09)	0.00 (0.00–0.02)	0.14 (0.09–0.21)
Age 16 years	0.10 (0.00–0.25)	0.17 (0.04–0.30)	0.00 (0.00–0.12)	0.25 (0.19–0.31)
Proportion of phenotypic variance and covariance accounted for by E
Age 4 years	0.41 (0.38–0.43)
Age 7 years	0.24 (0.20–0.28)	0.38 (0.36–0.40)
Age 9 years	0.21 (0.15–0.27)	0.30 (0.26–0.35)	0.32 (0.29–0.35)
Age 16 years	0.12 (.03–0.20)	0.24 (0.18–0.30)	0.28 (0.21–0.36)	0.42 (0.39–0.45)

Data are given as proportion (95% confidence interval).

A, Additive genetic parameters; C, shared environment parameters; E, non-shared environment parameters.

^aThe same pattern of results was found when we replicated the analyses using a stable index of obsessive–compulsive behaviour (i.e. the same three items at each age).