Table 2.

Age- and sex-adjusted pairwise twin correlations

	Number of pairs		Pairwise twin correlations (95% CI)
Phenotype	MZ	DZ	MZ	DZ
Ever-smokers versus never-smokers	2,647	5,356	0.87 (0.84–0.89)	0.62 (0.59–0.65)
Intermittent smokers versus regular smokers (among ever-smokers)	1,128	2,145	0.56 (0.36–0.71)	0.38 (0.22–0.52)
Intermittent smokers versus never-smokers (regular smokers excluded)	1,194	2,008	0.62 (0.42–0.76)	0.33 (0.16–0.47)

Note. DZ, dizygotic; MZ, monozygotic.