1. Netherlands Twin Register (NTR) 30,000 twin pairs registered at birth, born after 1986 Questionnaire variables Zygosity, health and growth2, 3, 5, 7, 10, 12, (14, 16) SES 3, 7, 10, 12 Problem behavior CBCL (Devereux at 5) 3, 5, 7, 10, 12 TRF 7, 10, 12 YSR 12, (14, 16) Motor development2, 5 School achievement 5, 12, (14, 16) Family Composition 5, 12, (14, 16) Seventeenth International Workshop On Methodology of Twin And Family Studies Boulder, CO, 2004

2. Aggressive and Rule-Breaking Behavior Seventeenth International Workshop On Methodology of Twin And Family Studies Boulder, CO, 2004

3. Table 1: CBCL-items of the syndrome Aggressive Behavior for the CBCL/2-3 and CBCL/4-18 Seventeenth International Workshop On Methodology of Twin And Family Studies Boulder, CO, 2004 Aggressive Behavior 10 year old twins rated by their mother skewness: 1.346

4. Table 1: CBCL-items of the syndrome Aggressive Behavior for the CBCL/2-3 and CBCL/4-18 Seventeenth International Workshop On Methodology of Twin And Family Studies Boulder, CO, 2004 Square root transformed Aggressive Behavior 10 year old twins rated by their mother skewness:.046

5. Table 1: CBCL-items of the syndrome Aggressive Behavior for the CBCL/2-3 and CBCL/4-18 Seventeenth International Workshop On Methodology of Twin And Family Studies Boulder, CO, 2004 SPSS descriptives PairsM a M b Var a Var b r MZM5142.412.381.621.56.84 DZM4672.242.311.621.50.50 MZF6091.981.901.311.28.79 DZF4521.951.911.361.26.54 DOS m-f 8852.231.811.571.29.47

6. Table 1: CBCL-items of the syndrome Aggressive Behavior for the CBCL/2-3 and CBCL/4-18 Seventeenth International Workshop On Methodology of Twin And Family Studies Boulder, CO, 2004 Mx Means and Variance (Saturated) Males-2LL dfparΔχ 2 dfpAIC means free5712.15 195610 eq means5716.90 195974.7553.191-1.245 eq m/ eq v5718.77 196246.6226.357-5.378 Females-2LL dfparΔχ 2 dfpAIC means free5844.97 212010 eq means5854.08 212379.1103.0283.11 eq m/ eq v5855.33 2126410.36060.110-1.64 eq v5846.23 212371.25730.139-4.74 Males/Females-2LL dfparΔχ 2 dfpAIC means free11557.121 407620 eq means11636.350 40831379.2297.00065.229 eq m/ eq v11652.008 4090694.88714.00066.887 eq v11572.401 40831315.2807.0331.280

7. Table 1: CBCL-items of the syndrome Aggressive Behavior for the CBCL/2-3 and CBCL/4-18 Seventeenth International Workshop On Methodology of Twin And Family Studies Boulder, CO, 2004 Mx Estimates of Means and Variances T 1 T 2 V T1 V T2 rr (eq m) MZF1.991.901.311.28.792.789 DZF1.951.911.361.26.538.537 MZM2.412.381.611.56.83 DZM2.242.301.611.49.50

8. Table 1: CBCL-items of the syndrome Aggressive Behavior for the CBCL/2-3 and CBCL/4-18 Seventeenth International Workshop On Methodology of Twin And Family Studies Boulder, CO, 2004 Mx Means and Variance (Saturated) SS and OS twins Males/Females-2LL dfparΔχ 2 dfpAIC 16997.749 5845 25 eq m ssm 17002.503 5848 224.7553.191-1.245 ss/os 17005.925 5849 218.1764.0850.176 eq m ssf17006.859 5848 229.1103.0283.110 ss / osf17012.611 5849 2114.8624.0056.862

9. Table 1: CBCL-items of the syndrome Aggressive Behavior for the CBCL/2-3 and CBCL/4-18 Seventeenth International Workshop On Methodology of Twin And Family Studies Boulder, CO, 2004 Model Fitting Results Boys -2LLdfχ 2 ΔdfACE ACE5713.8271959.67.17.16 AE5719.54219605.721.84-.16 CE5864.2351960150.41-.68.32 Girls -2LLdfχ 2 ΔdfACE ACE5846.2322123.52.28.21 AE5861.720212415.491.80-.20 CE5936.009212489.771-.68.32