‘Relative risk’ is:
**Core Concept**
Relative risk (RR) is a statistical measure used to compare the probability of an event occurring in one group to the probability of the same event occurring in another group. It is a key concept in epidemiology and biostatistics, used to assess the strength of association between a risk factor and a disease or outcome.
**Why the Correct Answer is Right**
Relative risk is calculated by dividing the incidence rate of the outcome in the exposed group by the incidence rate in the unexposed group. This allows researchers to quantify the increased or decreased risk of an outcome associated with a particular exposure. In clinical practice, relative risk is often expressed as a ratio, where a value of 1 indicates no association, a value greater than 1 indicates an increased risk, and a value less than 1 indicates a decreased risk.
**Why Each Wrong Option is Incorrect**
**Option A:** Odds ratio is a measure of association between an exposure and an outcome, but it is not a direct measure of risk.
**Option B:** Absolute risk is a measure of the probability of an outcome occurring in a specific population, but it does not compare the risk between two groups.
**Option C:** Number needed to harm (NNH) is a measure of the number of individuals who need to be exposed to a risk factor to cause one additional adverse outcome, but it is not a measure of relative risk.
**Clinical Pearl / High-Yield Fact**
When interpreting relative risk, it's essential to consider the absolute risk of the outcome in both groups. A small relative risk may still be clinically significant if the absolute risk is high.
**Correct Answer: D. Relative risk is a statistical measure used to compare the probability of an event occurring in one group to the probability of the same event occurring in another group.**