Explanation base rateTPFP Chance that Homer has X Disease X 1 in 191100%10% 5% Disease Y 1 in 11100%10%50% Disease X 191 1 has X 1 TP 190 do not 19 FPs 1 / 20 = 5% Disease Y11 1 has X1 TP 10 do not 1 FP 1 / 2 = 50%