ICCs for the TOCS total and dimension scores in the twins are shown in Table 3. No differences in the means and variances for the MZ and DZ twins were observed. For all variables, ICCs were larger for MZ than DZ twins, suggesting a genetic contribution to OC traits. MZ twin correlations were about double the DZ correlations across traits except for Cleaning/Contamination (Supplemental Table 6). Table 3 provides the standardized parameter estimates for the ACE or AE models. The small sample size resulted in low power to detect small effects. For example, heritability of the Cleaning/Contamination dimension was 30%, which is not negligible, but was not statistically significant (95% confidence interval: 0.0–0.66).Table 3Univariate heritability analyses of overall OC trait and dimensionsVariableICCBest fitting modelΔ AICΔ χ2Δ dfp -valueA (CI)C (CI)E (CI)MZ (CI) (N=120)DZ (CI) (N=320)TOCS Total Z score0.74 (0.60–0.83)0.37 (0.23–0.50)AE7.486.5270.480.74 (0.63, 0.82)n/a0.26 (0.18, 0.37) CBCL-OCS Total score0.62 (0.44–0.75)0.34 (0.20–0.47)AE4.959.0570.250.56 (0.40, 0.68)n/a0.44 (0.32, 0.60)TOCS dimensions Cleaning/Contamination0.56 (0.36–0.71)0.40 (0.27–0.53)ACE7.604.4060.620.30 (0, 0.66)0.26 (0, 0.52)0.45 (0.31, 0.63) Symmetry/Ordering0.72 (0.57–0.82)0.30 (0.15–0.43)AE8.675.3370.620.70 (0.57, 0.79)n/a0.30 (0.21, 0.43) Superstition0.70 (0.54–0.81)0.46 (0.33–0.58)ACE10.381.6260.950.50 (0.17, 0.78)0.20 (0, 0.44)0.29 (0.20, 0.43) Rumination0.55
