Relative risk is define as –
**Core Concept**
Relative risk (RR) is a statistical measure used in epidemiology to compare the likelihood of an event or outcome occurring in one group versus another. It is a ratio of the probability of an event occurring in the exposed group (those with a specific risk factor or condition) versus the non-exposed group (those without the risk factor or condition).
**Why the Correct Answer is Right**
Relative risk is calculated by dividing the probability of the event occurring in the exposed group by the probability of the event occurring in the non-exposed group. This ratio can be expressed as a number greater than 1, less than 1, or equal to 1, indicating an increased, decreased, or no change in risk, respectively. For example, if the RR of developing a disease is 2, it means that the exposed group is twice as likely to develop the disease as the non-exposed group.
**Why Each Wrong Option is Incorrect**
**Option A:** Odds ratio (OR) is a similar measure, but it is not the same as RR. OR is a ratio of the odds of an event occurring in the exposed group versus the non-exposed group.
**Option B:** Risk difference (RD) is the difference in risk between the exposed and non-exposed groups, not a ratio.
**Option C:** Attributable risk (AR) is the proportion of cases in the exposed group that can be attributed to the exposure, not a measure of relative risk.
**Clinical Pearl / High-Yield Fact**
When interpreting RR, it's essential to consider the baseline risk of the outcome in both groups. A high RR may not be clinically significant if the baseline risk is low, and a low RR may be significant if the baseline risk is high.
**Correct Answer: D.**