Ans. c (Number of true positives + number of false positives) (Ref. Park PSM 22nd/pg. 131).TopicEquation SensitivitySensitivity =a--a+cSpecificitySpecificity =d-b+dPositive predictive valuePPV =a--a + b Negative predictive valueNPV =d--c+d Relative riskRR =a--a + b c--c+d Attribute riskAR =a--a+bc--c+dHardy-Weinberg equilibriumP2 + 2pq + q2 =1p + q = lThe positive predictive value. or precision rate, is the proportion of patients with positive test results who are correctly diagnosed. It is considered the physician's gold standard, as it reflects the probability that a positive test reflects the underlying condition being tested for.Related calculationsFalse positive rate (a) = FP/(FP +TN) = 18/(18+182) = 90% = 1 - specificityFalse negative rate (b) = FN/(TP+FN) =1 (2+1) = 33% = 1 - sensitivityPower =1 - bDefinition:PPV =Number of True Positives-----------------------------------------Number of true positives + Number of False Positives or, alternatively.PPV =(Sensitivity) (prevalence)----------------------------------(Sensitivity) (prevalence) + (1 - specificity) (1 - prevalence)The negative predictive value is the proportion of patients with negative test results who are correctly diagnosed.NPV =Number of True Negatives----------------------------------------Number of True Negatives + Number of False Negatives or alternatively.NPV =Specificity x (1 - prevalence)----------------------------------Specificity x (1 - prevalence) + ( 1 - sensitivity) x prevalence