Table 3.

Estimated intraclass correlation coefficients across entire cohort (estimated N = 6,464) between the same language and nonverbal measures at Year 1 and Year 3

Measure	Intraclass correlation (Year 1–Year 3)	95% Confidence interval
1 Nonverbal IQ	0.834	0.800, 0.863
2 Vocabulary	0.912	0.893, 0.927
3 Grammar	0.909	0.890, 0.925
4 Narrative	0.817	0.783, 0.847
5 Receptive	0.894	0.870, 0.915
6 Expressive	0.916	0.895, 0.932
7 Total language	0.940	0.926, 0.951

Note: All tests were the same except nonverbal ability, in which matrix reasoning from the WPPSI was used at Year 1 and from the WISC at Year 3