To estimate the heritability of each of the clusters, logistic regression was first used to construct a classifier to separate subjects in each of the different clusters. The resultant classifier, as a function of the 69 measures of opioid use and related behaviors, calculated the likelihood that each subject belonged to a specific cluster. The log likelihood of 4,964 subjects from EA and AA populations with 1,805 of them from multi-member families was submitted to Sequential Oligogenic Linkage Analysis Routines (SOLAR) (Almasy and Blangero, 1998) software together with pedigrees to estimate the heritability of the cluster-derived trait. Including singleton cases together with multi-member families in the heritability estimation helped to correct the bias in the family-based sample due to the ascertainment method and is the preferred approach (Almasy and Blangero, 1998). Sex, age, and race were used as covariates in the heritability estimate.
