## **Core Concept**
Relative risk (RR), also known as the risk ratio, is a measure used in epidemiology to compare the risk of a certain event (such as developing a disease) occurring in one group with the risk of the same event occurring in another group. It is calculated by dividing the probability of an event occurring in the exposed group versus a non-exposed group.

## **Why the Correct Answer is Right**
The formula for relative risk is:
[ RR = frac{P(text{event}|text{exposed})}{P(text{event}|text{non-exposed})} ]
Where:
- ( P(text{event}|text{exposed}) ) is the probability of the event occurring in the exposed group,
- ( P(text{event}|text{non-exposed}) ) is the probability of the event occurring in the non-exposed group.

## **Why Each Wrong Option is Incorrect**
- **Option A:**
This option does not represent a valid formula for relative risk. It seems to confuse the formula with something else used in statistics or epidemiology.
- **Option B:**
This option is incorrect because it does not accurately represent the formula for relative risk. It might be confusing with odds ratio or another statistical measure.
- **Option D:**
This option seems to represent a misunderstanding or misrepresentation of the relative risk formula. It does not accurately reflect how relative risk is calculated.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that relative risk is used in cohort studies to describe the strength of association between a particular risk factor and a specific outcome. A relative risk of 1 means there is no difference in risk between the two groups. A relative risk greater than 1 indicates an increased risk, and a relative risk less than 1 indicates a decreased risk.

## **Correct Answer:** C.