Similarity analyses and prediction of immunoassay cross-reactivity for synthetic cannabinoids of the JWH series. Similarity analyses for ELISA assays of JWH-018 and JWH-250 - (A) 2D similarity of compounds that are cross-reactive (divided into sub-categories of 25% or greater and 1-24%), non-cross-reactive, or untested for a JWH-018 Direct ELISA . The 5-hydroxy metabolite of JWH-018 is used as the target for similarity analysis. (B) ROC curve analysis for the ability of 2D similarity to predict the cross-reactivity of compounds for the JWH-018 ELISA. The AUC is 0.987. Maximum efficiency of 82.1% is achieved at a cutoff of 0.673 (sensitivity = 93.8% and specificity = 56.7% at that cutoff). (C) 2D similarity of compounds that are cross-reactive, non-cross-reactive, or untested for a JWH-250 Direct ELISA . The 4-hydroxy metabolite of JWH-250 is used as the target for similarity analysis.