As a measure of the overall predictive power, the logistic regression concordance rate (C) was computed for each of the top findings in Tables 2 and 3 – the reported ΔC parameter is the difference in concordance rates between the genetic model (equations 2 or 3 for Tables 2 and 3, respectively) and the base model (equation 1). A “leave-one-out” cross-validation approach was employed to reduce overfitting (i.e, risk for each observation is predicted from model parameterized on all other observations). For the main effect models, ΔC values ranged from 0.18 to 0.50 with a median of 0.28%, whereas for the interaction model ΔC values ranged from 0.18 to 0.72, with a median value of 0.40%.
