TABLE 2.

Number of Twin Families and Means, Standard Deviations, and Regression Coefficients (β) With 95% Confidence Intervals (CI) of Maternal and Paternal Education By Zygosity and Birth Cohort

Birth cohort	MZ twins			DZ twins			Regression coefficient1
	N	Mean	SD	N	mean	SD	β	95% CI
Maternal education
1890–1899	8	8.3	2.49	5	8.2	3.90	−0.05	−3.91, 3.81
1900–1909	75	9.5	2.94	96	9.0	3.03	−0.44	−1.36, 0.47
1910–1919	713	9.3	3.07	826	9.3	2.91	−0.03	−0.33, 0.26
1920–1929	2,095	9.7	3.05	2,459	9.5	3.00	−0.31	−0.48, −0.13
1930–1939	1,267	10.4	2.69	1,864	10.4	2.75	−0.08	−0.27, 0.11
1940–1949	2,794	11.0	2.62	4,763	11.1	2.72	−0.11	−0.22, 0.01
1950–1959	4,427	11.5	2.82	6,375	11.6	2.66	−0.12	−0.22, −0.03
1960–1969	1,956	12.0	3.35	2,478	12.6	3.00	0.10	−0.06, 0.27
1970–1979	2,451	12.2	3.37	2,997	12.3	3.17	0.10	−0.06, 0.26
1980–1989	3,164	12.9	3.26	4,319	12.6	3.50	0.06	−0.09, 0.21
1990–1999	7,009	13.9	2.90	12,909	14.1	2.92	0.06	−0.01, 0.14
2000 or later	4,280	15.2	3.04	9,418	15.3	3.18	0.06	−0.04, 0.16
Paternal education
1890–1899	9	7.3	2.00	4	7.5	1.91	0.17	−2.44, 2.78
1900–1909	67	9.8	3.69	89	9.0	3.37	−0.82	−1.95, 0.31
1910–1919	675	9.6	3.49	800	9.5	3.47	−0.05	−0.40, 0.31
1920–1929	2,018	9.7	3.65	2,378	9.5	3.42	−0.31	−0.52, −0.10
1930–1939	1,219	10.4	3.08	1,781	10.3	3.06	−0.08	−0.30, 0.14
1940–1949	2,724	11.0	3.07	4,626	11.0	3.19	−0.06	−0.21, 0.08
1950–1959	4,290	11.7	3.34	6,224	11.8	3.24	−0.18	−0.30, −0.06
1960–1969	1,869	12.8	3.66	2,365	13.1	3.36	−0.05	−0.25, 0.16
1970–1979	2,308	12.7	3.48	2,765	12.6	3.35	0.07	−0.11, 0.24
1980–1989	2,980	12.9	3.60	4,090	12.5	3.88	0.08	−0.08, 0.24
1990–1999	6,875	13.9	3.03	12,665	14.2	3.06	0.16	0.08, 0.25
2000 or later	4,114	14.8	3.34	9,089	15.0	3.34	0.11	0.00, 0.22

Note:

¹Adjusted for twin cohort; MZ twins used as the reference category.