Validation of the multiple regression model. The solid line illustrates perfect prediction in the pilot cohort and the dashed reference lines show deviation from the prediction of plus or minus 1.25 mg (½, pill) and plus or minus 2.5 mg (1 pill) per day. Predictors: VKORC1 rs9923231, CYP2C9 *2 and *3, age, sex, and drug interactions. rs9923231 is used in this algorithm since it is possibly functional.