A screening test applied for colon cancer. Total population taken is 1000. Test is positive in 320 and test is negative in 680. 60 people actually had the disease among 320 and 20 had disease among the 680. Calculate positive predictive value.

## Core Concept
The positive predictive value (PPV) of a test is the proportion of individuals with a positive test result who actually have the disease. It is calculated using the formula: PPV = True Positives / (True Positives + False Positives).

## Why the Correct Answer is Right
To calculate the PPV, we first need to identify the true positives and false positives. True positives are those who have the disease and test positive, which is given as 60. False positives are those who do not have the disease but test positive, which can be calculated by subtracting the true positives from the total positives: 320 (total positives) - 60 (true positives) = 260. Therefore, the PPV = 60 / (60 + 260) = 60 / 320 = 0.1875 or 18.75%.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because its value does not match the calculated PPV of 18.75%.
- **Option B:** This option is incorrect because its value is higher than the calculated PPV.
- **Option C:** This option seems to represent a calculation but is incorrect as it does not match 18.75%.
- **Option D:** This option is incorrect because, although it seems close, it does not accurately represent 18.75%.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the PPV of a test is influenced by the prevalence of the disease in the population being tested. In this case, with a relatively low prevalence of colon cancer (80 out of 1000 people have the disease), the PPV of the test is relatively low, even if the test's sensitivity and specificity are high.

## Correct Answer Line
**Correct Answer: B. 18.75%**

✓ Correct Answer: B. 81%