. Author manuscript; available in PMC: 2014 Jan 1.

Published in final edited form as: Arch Sex Behav. 2012 Mar 23;42(1):35–44. doi: 10.1007/s10508-012-9947-1

Table 2.

Twin-Pair Similarity for Measured Variables

			r^a(SE)
			Within-pair similarity
Variable	N	% of pairs discordant	MZ pairs	DZ pairs
Early intercourse	3,822	20.0%	0.78 (0.02)	0.53 (0.04)
Adverse childhood experiences	3,989	17.0%	0.71 (0.03)	0.58 (0.04)
Early cigarette use	3,297	11.2%	0.60 (0.05)	0.34 (0.07)
Early cannabis use	5,611	3.1%	0.65 (0.06)	0.58 (0.07)

Note: N = number of twin pairs in which both twins provided data.

Tetrachoric correlation (r) representing twin liability for exposure based on co-twin exposure.