Total population having the disease : ‘a + c’ (TP + FN) Total population not having the disease : ‘b + d’ (FP + TN) Total population: a + b + c + d = TP + FP + FN + TNPPV depends on sensitivity, specificity and prevalence of disease in the population. Now in this question, a screening test is used in same way in two similar populations; thereby the screening test will have similar sensitivity and specificity in both populations. PPV = a/ (a + (b) X 100, thus b (False Positive rate) is inversely proportional to PPV; and PPV is directly proportional to Prevalence of disease in a population. So, False Positive rate (FP rate) is inversely proportional to the prevalence of disease in the population. Therefore, if the same screening test is having lower FP rate in population A (as compared to a similar population B), then this could be explained by higher prevalence of disease in population A Also,