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. Author manuscript; available in PMC: 2022 Aug 9.
Published in final edited form as: Psychol Med. 2016 Jul 27;46(14):2919–2930. doi: 10.1017/S0033291716001525

Fig. 1.

Fig. 1.

A model quantifying the extent to which the genetic and environmental covariation between major depressive disorder (MDD) and alcohol use disorder (AUD) is explained by (1) additive genetic and unique environmental factors that influence stress reaction (SR), (2) additive genetic and unique environmental factors that influence behavioral control (CON), and (3) additive genetic and unique environmental factors that influence both SR and CON. For simplicity, this model is illustrated for only one individual from a twin pair. In this model, SR is entered first; thus, the proportion of genetic covariation between MDD and AUD that is attributable to CON (after accounting for genetic variation shared with SR) is [(a23 × a24)/(a13 × a14 + a23 × a24 + a33 × a34)]. To determine the proportion of genetic covariation attributable to SR (after accounting for genetic variation shared with CON), this model was re-run with CON entered first.