. Author manuscript; available in PMC: 2014 May 9.

Published in final edited form as: Behav Genet. 2013 Feb 10;43(3):208–219. doi: 10.1007/s10519-012-9581-7

Table 6.

Age descriptives, heritability, standardized parameter estimates, and number of MZ and DZ twins within each age category for both the aggregated data and the data within each study.

Cat	Study	N_MZ	N_DZ	Age		Heritability	Variance of A	Variance of E Baseline and AxE parameter		Variance of C	χ²(1)

				mean	sd	h²	σ_A²	β₀ (baseline)	β₁ (AxE)	σ_C²
4–10	Netherlands #1	125	112	5.80	0.06	0.43	0.42 (0.18; 0.68)	−1.43 (−1.77; −1.13)	−0.70 (−1.09; −0.34)	0.26 (0.03; 0.50)	14.62
	Netherlands #2	49	63	9.10	0.10	0.53	0.52 (0.18; 0.98)	−1.54 (−1.92; −1.11)	−0.16 (−0.64; 0.29)	0.24 (0.00; 0.60)	0.53
	Colorado #1	391	534	8.92	0.80	0.64	0.65 (0.51; 0.84)	−1.82 (−2.04; −1.59)	0.42 (−0.17; 0.68)	0.19 (0.05; 0.32)	2.65
	Ohio	121	171	6.07	0.68	0.42	0.42 (0.21; 0.65)	−1.46 (−1.71; −1.20)	0.13 (−0.19; 0.46	0.34 (0.12; 0.55)	0.62
	UK	394	714	10.59	0.24	0.32	0.32 (0.18; 0.46)	−1.21 (−1.37; −1.06)	−0.53 (−0.72; −0.37)	0.34 (0.22; 0.45)	42.52

	Aggregated	1140	1616	9.06	1.79	0.42	0.41 (0.34; 0.49)	−1.42 (−1.52; −1.33)	−0.33 (−0.45; −0.22)	0.34 (0.26; 0.41)	33.98

11–13	Netherlands #3	79	111	12.02	0.08	0.64	0.64 (0.41; 0.87)	−1.95 (−2.25; −1.62)	−0.02 (−0.49; 0.51)	0.21 (0.00; 0.47)	0.01
	Colorado #1	204	280	11.85	0.81	0.65	0.64 (0.50; 0.80)	−2.06 (−2.26; −1.85)	0.14 (−0.13; 0.43)	0.22 (0.08; 0.38)	1.01
	Minnesota #1	734	453	11.82	0.40	0.49	0.49 (0.36; 0.62)	−1.44 (−1.55; −1.33)	0.23 (−0.001; 0.42)	0.27 (0.14; 0.40)	3.82
	UK	1135	1818	11.78	0.40	0.50	0.49 (0.41; 0.57)	−1.37 (−1.47; −1.28)	−0.73 (−0.83; −0.64)	0.16 (0.09; 0.23)	306.29

	Aggregated	2195	2720	11.83	0.47	0.56	0.52 (0.46; 0.59)	−1.45 (−1.52; −1.38)	−0.52 (−0.60; −0.45)	0.21 (0.15; 0.27)	203.10

14–16	Colorado #1	126	173	14.74	0.77	0.80	0.79 (0.63; 0.93)	−2.12 (−2.36; −1.86)	0.09 (−0.26; 0.46)	0.08 (0.02; 0.26)	0.27
	Colorado #2	153	125	16.00	0.00	0.75	0.76 (0.49; 0.96)	−2.03 (−2.31; −1.76)	0.57 (0.25; 0.93)	0.10 (0.02; 0.36)	11.58
	Colorado #3	99	140	14.75	0.84	0.54	0.54 (0.28; 0.81)	−1.54 (−1.97; −1.21)	−0.33 (−0.95; 0.12)	0.24 (0.00; 0.50)	1.89
	Minnesota #2	92	31	16.84	0.10	0.81	0.77 (0.62; 0.93)	−1.70 (−1.95; −1.42)	0.19 (−0.16; 0.52)	0.00 (0.00; 0.34)	1.13
	Australia	324	483	15.93	0.26	0.73	0.72 (0.59; 0.82)	−1.75 (−1.91; −1.59)	−0.24 (−0.45; −0.03)	0.09 (0.02; 0.22)	5.12

	Aggregated	807	966	15.66	0.81	0.71	0.71 (0.63; 0.78)	−1.77 (−1.86; −1.67)	−0.05 (−0.20; 0.10)	0.12 (0.06; 0.20)	0.41

17–34	Netherlands #4	66	94	17.62	0.38	0.80	0.85 (0.62; 1.00)	−1.93 (−2.28; −1.55)	−0.11 (−0.53; 0.35)	0.06 (0.00; 0.23)	0.24
	Colorado #3	203	180	19.46	2.00	0.53	0.53 (0.36; 0.73)	−1.85 (−2.11; −1.61)	−0.38 (−0.74; −0.05)	0.31 (0.11; 0.50)	4.94
	Minnesota #2	318	183	17.63	0.36	0.57	0.56 (0.38; 0.76)	−1.76 (−1.97; −1.57)	0.53 (0.27; 0.82)	0.23 (0.07; 0.43)	17.21

	Aggregated	700	615	18.78	2.71	0.69	0.69 (0.57; 0.80)	−1.77 (−1.88; −1.65)	0.19 (0.01; 0.37)	0.14 (0.05; 0.26)	4.39

Note. χ²(1) denotes a likelihood ratio test on parameter β₁. 95% confidence intervals are in brackets.

In a few cases we experienced numerical difficulties in estimating the lower bound of γ₀ because the number of DZ twins was too small. ‘Aggregated’ is based on the aggregated data within the corresponding age category including the Netherlands #5 and Netherlands #6 studies. As some samples are omitted in the analysis of the individual studies (see Table 2), N_MZ and N_DZ will not necessarily add up to the aggregated N_MZ and N_DZ.