Table 2.

Tetrachoric twin correlations by sex and sample

		MZ M	DZ M	MZ F	DZ F	DZ OS
RSI	Netherlands	0.86	0.52	0.82	0.55	0.49
	Finland	0.78	0.71	0.85	0.67	0.40
	Minnesota	0.76	0.51	0.77	0.54	NA
CI	Netherlands	0.73	0.64	0.73	0.49	0.51
	Finland	0.74	0.47	0.83	0.61	0.33
	Minnesota	0.84	0.60	0.69	0.73	NA

Note MZ refers to monozygotic pairs; DZ refers to dizygotic pairs; M refers to same-sex male pairs; F refers to same-sex female pairs; OS refers to opposite-sex dizygotic pairs; RSI refers to regular smoking initiation; CI refers to cannabis initiation