Table 2. Phenotypic correlations between IQ measures.

Age	2	3	4	7	9	10	12	14
2
3	0.64
	(0.62–0.66)
4	0.54	0.69
	(0.52–0.56)	(0.67–0.71)
7	0.25	0.26	0.30
	(0.22–0.28)	(0.23–0.29)	(0.27–0.33)
9	0.19	0.23	0.26	0.43
	(0.15–0.23)	(0.19–0.27)	(0.22–0.30)	(0.40–0.46)
10	0.20	0.21	0.23	0.42	0.56
	(0.16–0.24)	(0.17–0.25)	(0.19–0.27)	(0.38–0.45)	(0.53–0.59)
12	0.16	0.20	0.24	0.45	0.52	0.59
	(0.12–0.20)	(0.16–0.24)	(0.21–0.27)	(0.42–0.48)	(0.49–0.55)	(0.56–0.62)
14	0.17	0.19	0.19	0.44	0.47	0.51	0.61
	(0.12–0.22)	(0.14–0.24)	(0.15–0.23)	(0.40–0.48)	(0.43–0.51)	(0.47–0.55)	(0.58–0.64)

Correlations are based on one randomly selected member of each twin pair.