This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
In a village having population of 1000, we found patients with ceain disease. The results of a new diagnostic test on that disease are also follows: Test Result: Disease Present Present + 180 400 - 20 400 What is the percent prevalence of disease? 
Select and explain. 
A. 0.2, B. 2, C. 18, D. 20
D: 20
Answer: D: 20 
Explanation: Village population = 1000 Total disease person = 180+20 = 200 In this 180 true positive so 20(200-180) false negative by test. But we want only percentage prevalence of disease only. Prevalence = (200/1000) x 100 = 20% Prevalence of disease is 20% in village % prevalence of disease by using diagnostic test used = (180/1000) x 100 = 18% Ref: Park's Textbook Of Preventive And Social Medicine By K. Park, 17th Edition, Page 56; Park's Textbook Of Preventive And Social Medicine By K. Park, 18th Edition, Page 55