This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Screening, Subject name: Social & Preventive Medicine
A test has a high false positive rate in a community. True is 
Select and explain. 
A. High prevalence, B. Low prevalence, C. High sensitivity, D. High specificity
B: Low prevalence
Answer: B: Low prevalence 
Explanation: The propoion of false-positive results among those who test positive is 1 minus the positive predictive value. False positive (discovery) rate = 1- positive predictive valueAs the disease prevalence increases, the positive predictive value increases. (PPV)As prevalence increase, PPV increase, False positive rate decrease.