Fig. 4. ARPA for the Kentucky sample.

a Derived CART tree for SUD status as categorical target variable (disjunctive affection status, i.e., substance use of either alcohol, or nicotine, or other drugs). This derived tree for the Kentucky sample included demographic (sex), clinical (high Body Mass index [HBMI], and schizophrenia diagnosis), and genetic variables (markers rs4860437 and rs7659636). Notably, the T allele of the rs4860437 variant generated a split in the same direction as occurred for the derived tree in the Paisa and in the Spain samples. b Variable importance scores derived by Random Forest and TreeNet analysis were compatible with the variables included in the tree derived by CART. c, d TreeNet analysis to maximize ROC area and minimize classification error using 200 trees. The AUC were 0.811 and 0.744 for learning and testing samples, respectively, while the proportions of misclassification for SUD cases in the cross-validation experiment, for learning and testing data were 0.285 and 0.252, respectively. Conventions as in Fig. 1