Denominator for calculating Positive Predictive Value?
Ans. C. True positives + False positives. (Ref. Park's Textbook of PSM 22nd//pg.l31)Discussion:Screening test resultsDiagnosis Total DiseasedNot diseased Positivea (True Positive)b (False Positive)a + bNegativec (False Negative)d (True Negative)c+ 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 = a/a + c X 100Specificity- Ability of a test to identify correctly those who do not have the disease that is TRUE NEGATIVE = d/b + 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.
True positives + false negatives
False positives + true negatives
True positives + False positives
True negatives + Flase negatives
Screening for Disease