Table 2.

Twin correlations for cognitive ability, with their 95% confidence interval, for the entire sample and the three maternal educational subgroups

	MZ	DZ
Entire sample	.83 (.81–.84) n = 1,192 pairs	.45 (.41–.48) n = 1,938 pairs
Low education	.84 (.81–.86) n = 404 pairs	.40 (.34–.47) n = 690 pairs
Middle education	.78 (.75–.81) n = 506 pairs	.37 (.31–.43) n = 809 pairs
High education	.82 (.79–.85) n = 282 pairs	.39 (.31–.47) n = 439 pairs