Table 3—

Twin correlations, cross-trait correlations and cross-trait, cross-twin correlations for asthma, eczema and rhinitis across zygosity and sex groups

	MZM	DZM	MZF	DZF	OS-mf	OS-fm
Twin pairs n	1286	1394	1509	1343	1392	1346
Twin correlations
Asthma	0.89	0.37	0.92	0.47	0.40	0.44
Eczema	0.83	0.27	0.85	0.32	0.24	0.36
Rhinitis	0.93	0.55	0.97	0.37	0.61	0.54
Within-twin, cross-trait correlations
Asthma–eczema	0.45	0.34	0.37	0.33	0.35	0.28
Asthma–rhinitis	0.48	0.48	0.49	0.52	0.44	0.52
Eczema–rhinitis	0.38	0.43	0.37	0.35	0.32	0.41
Cross-trait, cross-twin correlations
Asthma–eczema	0.43	0.05	0.34	0.18	0.09	0.06
Asthma–rhinitis	0.38	0.21	0.43	0.28	0.19	0.18
Eczema–rhinitis	0.35	0.17	0.35	0.15	0.25	0.15

MZM: monozygotic male twin pairs; DZM: dizygotic male twin pairs; MZF: monozygotic female twin pairs; DZF: dizygotic female twin pairs; OS-mf: opposite sex twin pairs, with male as the first born and female as the second born; OS-fm: opposite sex twin pairs, with female as the first born and male as the second born.