Table II.

Model fit comparisons within the full bivariate ACE model examining qualitative and quantitative sex differences.

Model	Model Description	Estimated Parameters	−2LL	df	AIC	Δ(−2LL)	Δdf	p	Comparison Model
1	Sex limitation, qual. on A and quant. sex-differences	25	28985.38	10940	7105.38	NA	NA	NA	NA
2	Sex limitation, qual. on C and quant. sex-differences	25	28986.23	10940	7106.23	0.85	0	NA	1
3	Scalar sex limitation, quant. sex-differences	20	28986.93	10945	7096.93	1.55	5	0.91	1
4	Homogeneity, no qual. nor quant. sex-differences	13	29003.10	10952	7099.10	17.72	12	0.12	1
4	Homogeneity, no qual. nor quant. sex-differences	13	29003.10	10952	7099.10	16.17	7	0.02	3

Note: Models 1-4 include common paths for correlated factors a, c, and e. A=Additive genetic component, C=Common/Shared environmental component, E=Unique environmental component, qual.=qualitative, quant.=quantitative. Best fitting model is designated in bold text. All five twin groups are included in the modeling (MZ female, MZ male, DZ female, DZ male, DZ opposite sex). Best fitting model denoted in bold.