In a village having population of 1000, we found patients with ceain disease. The results of new diagnostic test on disease are as follows: Test result Disease Present Absent + 180 400 – 20 400 What is the percent prevalence of disease?

**Core Concept**
The question tests the understanding of epidemiological principles, specifically the calculation of **prevalence** of a disease in a population. Prevalence is defined as the total number of cases of a disease present in a population at a given time.

**Why the Correct Answer is Right**
To calculate the percent prevalence, we need to know the total number of individuals with the disease (both true positives and false negatives) and the total population. From the given data, the total number of individuals with the disease is 180 (true positives) + 20 (false negatives) = 200. The total population is 1000. Thus, the percent prevalence is (200/1000) * 100 = 20%.

**Why Each Wrong Option is Incorrect**
**Option A:** This option would be incorrect because it does not correctly calculate the prevalence based on the provided data.
**Option B:** This option is also incorrect as it does not accurately reflect the calculation of prevalence.
**Option C:** Similarly, this option is wrong because it does not represent the correct formula or calculation for prevalence.
**Option D:** This is not the correct answer because the calculation provided does not match the definition of prevalence.

**Clinical Pearl / High-Yield Fact**
Remember, **prevalence** is a measure of the total burden of a disease in a population, and it is calculated as the number of cases of the disease divided by the total population, usually expressed as a percentage.

**Correct Answer:** Correct Answer: C. 20%.