<prompt> Denominator for calculating Positive Predictive Value?True positives false negativesFalse positives true negativesTrue positives False positivesTrue negatives Flase negatives  <response>: Ans. C. True positives False positives. Ref. Parks Textbook of PSM 22ndpg.l31Discussion:Screening test resultsDiagnosis Total DiseasedNot diseased Positivea True Positiveb False Positivea bNegativec False Negatived True Negativec dTotala cb da b c dPredictive value of a positive test - indicates the probability that a patient with a positive test result has in fact disease in question. a a b X 100Predictive value of a negative test d c d X 100Sensitivity -Ability of a test to identify correctly all those who have the disease that is TRUE POSITIVE aa c X 100Specificity- Ability of a test to identify correctly those who do not have the disease that is TRUE NEGATIVE db d X 100False negatives c a c X 100False positive b b d X 100Always remember the table. For calculating Predictive value of a positive test and Predictive value of a negative test we take row total. For rest we take column total. 