Table 1.

Univariate twin correlations (within-trait cross-twin) and univariate twin model parameter estimates for IBD and allergic diseases in all 5 twin subcohorts combined (MZ twin pairs: n = 13 028, DZ twin pairs: n = 25 605)

	Twin correlations (95%CI)		Model	Twin model estimates (95% CI)a
	rMZ	rDZ		a2	c2 or d2	h2	e2	AIC
IBD	0.72 (0.66 to 0.77)	0.46 (0.39 to 0.52)	ACE ADE AEb	0.54 (0.30 to 0.79) 0.75 (0.68 to 0.82) 0.75 (0.68 to 0.82)b	0.18 (−0.01 to 0.38) 0.00 (0.00 to 0.00) —	— 0.75 (0.68 to 0.82) —	0.27 (0.19 to 0.35) 0.25 (0.18 to 0.32) 0.25 (0.18 to 0.32)b	5037.76 5039.08 5037.08b
Asthma	0.71 (0.69 to 0.72)	0.39 (0.37 to 0.40)	ACEb ADE AE	0.66 (0.59 to 0.72)b 0.72 (0.70 to 0.74) 0.72 (0.70 to 0.74)	0.06 (0.00 to 0.11)b 0.00 (0.00 to 0.00) —	— 0.66 (0.59 to 0.72) —	0.28 (0.26 to 0.31)b 0.28 (0.26 to 0.30) 0.28 (0.26 to 0.30)	26 866.73b 26 869.75 26 867.75
Allergic rhinitis	0.52 (0.50 to 0.54)	0.28 (0.26 to 0.29)	ACE ADE AEb	0.49 (0.42 to 0.56) 0.53 (0.51 to 0.55) 0.53 (0.51 to 0.55)b	0.03 (−0.02 to 0.09) 0.00 (0.00 to 0.00) —	— 0.53 (0.51 to 0.55) —	0.48 (0.45 to 0.51) 0.47 (0.45 to 0.49) 0.47 (0.45 to 0.49)b	36 249.36 36 250.61 36 248.61b
Eczema	0.43 (0.40 to 0.46)	0.23 (0.21 to 0.25)	ACE ADE AEb	0.43 (0.34 to 0.53) 0.44 (0.41 to 0.47) 0.44 (0.41 to 0.47)b	0.01 (−0.06 to 0.08) 0.00 (0.00 to 0.00) —	— 0.44 (0.41 to 0.47) —	0.56 (0.52 to 0.60) 0.56 (0.53 to 0.59) 0.56 (0.53 to 0.59)b	28 461.62 28 462.43 28 460.63b

Abbreviations: a², additive genetic component; AIC, Akaike information criterion; c², shared environmental component; CI, confidence interval; d², nonadditive/dominant genetic component; DZ, dizygotic; e², nonshared environmental component (including measurement errors); h², broad-sense heritability component (a² + d²); IBD, inflammatory bowel disease; MZ, monozygotic.

^aAll models were adjusted for sex and birth year (continuous, standardized).

^bBest fitting models and estimates.