(E; environmental influences not shared by twins and error variance). A is indicated when the MZ twin correlation (rMZ) > DZ twin correlation (rDZ), D when rDZ < ½ rMZ, and C when rDZ > ½ rMZ. E is based on the extent to which rMZ < 1.0. Thresholds (i.e., prevalences) were adjusted for age at Wave 4 using a median split (≥ 22 vs. <22 years; to avoid assumptions of linear relationships with age). Initially, EA and AA women were modeled simultaneously with variance components (A, C, E) and prevalences allowed to differ across racial/ethnic groups for all measures (e.g., AEA ≠ AAA). Racial/ethnic differences in the variance components were tested by constraining them to be equal (e.g., does AEA = AAA), and individual parameters (A, C, E) were constrained to zero to determine the significance of their contribution to the variance in and covariance between cannabis use or problems and childhood maltreatment. Relative model fit was computed using the difference in –2 log likelihood fit, which represents a χ2 distribution for the given degrees of freedom.
