Table 2.

Cross sectional analysis of LTL in relation to age, sex and twin sex composition (opposite sex vs same sex)

A. Baseline and follow-up combined, DZ and MZ combined, n=1534, R2=0.98
Parameter	Estimate (SE)	F	DF denominator	P
Intercept	7.752 (0.0466)
Age	−0.0186 (0.0005)	1309.10	787.3	<0.0001
Sex	−0.1643 (0.0615)	7.14	402.0	0.008
Opposite sex (OS)	−0.2378 (0.0818)	8.46	492.9	0.004
Sex * OS	0.1952 (0.0808)	5.84	775.3	0.016

B. Baseline and follow-up combined, DZ twins only, n=845, R2=0.98
Parameter	Estimate (SE)	F	DF denominator	P
Intercept	7.685 (0.0651)
Age	−0.0175 (0.0007)	608.12	433.4	<0.0001
Sex	−0.1911 (0.0876)	3.58	276.0	<0.06
Opposite sex (OS)	−0.2229 (0.0909)	2.57	222.5	0.11
Sex * OS	0.2230 (0.1082)	4.25	402.1	0.04

C. Baseline, DZ twins only, n=433, R2=0.76
Parameter	Estimate (SE)	F	DF denominator	P
Intercept	7.800 (0.156)
Age	−0.0203 (0.0038)	28.09	219.8	<0.0001
Sex	−0.1649 (0.0916)	3.24	221.4	0.073
Opposite sex (OS)	−0.2489 (0.0956)	6.78	283.9	<0.01
Sex * OS	0.1993 (0.1147)	3.02	401.7	0.083

D. Follow-up, DZ twins only, n=412, R2=0.81
Parameter	Estimate (SE)	F	DF denominator	P
Intercept	7.792 (0.1998)
Age	−0.0198 (0.0038)	27.19	219.6	<0.0001
Sex	−0.1913 (0.0889)	4.63	221.6	0.033
Opposite sex (OS)	−0.1864 (0.0917)	4.14	267.6	0.043
Sex * OS	0.2106 (0.1082)	3.79	375.7	0.052

Sex was coded 0 (females) and 1 (males). Opposite sex was also coded 0 (same sex) and 1 (opposite sex). Twin identity was included as random effect in all tables, with individual identity nested in twin identity added as random effect in tables A and B.

Note the similarity of the Sex * OS estimate in all data selections. Numerator DF=1 in all cases.