. 2022 Aug 24;118(1):110–118. doi: 10.1111/add.16016

TABLE 3.

Results of individual‐level mixed model and zygosity‐stratified co‐twin control mixed models

Individual‐level model				Twin models
Param.	Individual			Param.	All twins			Same‐sex dizygotic twins			Monozygotic twins
Param.	B	95% CI	P	Param.	B	95% CI	P	B	95% CI	P	B	95% CI	P
Int.	2.46	1.91, 3.00	1.38e⁻¹⁸	Int.	2.54	1.92, 3.15	1.24e⁻¹⁵	2.20	1.08, 3.32	1.30e⁻⁴	2.47	1.67, 3.26	1.65e⁻⁹
Legal status	0.21	0.11, 0.32	8.08e⁻⁵	Between‐pair	0.16	0.02, 0.29	0.024	0.31	0.06, 0.55	0.013	0.05	−0.14, 0.23	0.624
Legal status	0.21	0.11, 0.32	8.08e⁻⁵	Within‐pair	0.17	0.06, 0.29	0.002	0.19	−0.03, 0.40	0.096	0.18	0.04, 0.32	0.014
Age	−0.04	−0.05, −0.02	7.61e⁻⁷	Age	−0.04	−0.05, −0.02	3.38e⁻⁶	−0.04	−0.07, −0.01	0.006	−0.03	−0.05, −0.01	0.001
Sex	−0.32	−0.43, −0.22	2.02e⁻⁰⁹	Sex	−0.32	−0.44, −0.20	1.30e⁻⁷	−0.11	−0.33, 0.10	0.300	−0.33	−0.50, −0.17	7.78e⁻⁵
Intake cohort	0.22	−0.01, 0.44	0.059	Intake cohort	0.31	0.06, 0.57	0.017	0.46	0.05, 0.87	0.027	0.25	−0.10, 0.59	0.159
Pre‐2014 use	0.02	0.016, 0.018	5.04e⁻¹⁵¹	Pre‐2014 Use	0.02	0.016, 0.019	2.80e⁻¹²¹	0.02	0.015, 0.020	1.01e⁻⁴⁴	0.02	0.015, 0.019	1.06e⁻⁶⁰

The minimal attenuation between the individual‐level effect for legal status and co‐twin within‐pair effects indicates minimal genetic and shared environmental confounding. Param. = parameter; Int. = intercept; B = unstandardized regression parameter estimate; 95% CI = confidence interval; P = exact P‐value.