**Core Concept**
Relative risk (RR) is a statistical measure used to compare the likelihood of an event or outcome between two groups, typically an exposed group and a non-exposed group. It is calculated as the ratio of the incidence of the event in the exposed group to the incidence in the non-exposed group. RR is a useful measure for assessing the strength of association between a risk factor and an outcome.

**Why the Correct Answer is Right**
Relative risk can be obtained from a case-control study, where the incidence of the outcome is compared between the exposed and non-exposed groups. In a case-control study, the outcome (disease or condition) has already occurred, and the study aims to identify the risk factors that may have contributed to its development. By comparing the incidence of the outcome in the exposed and non-exposed groups, researchers can calculate the relative risk of developing the outcome in the presence of the risk factor.

**Why Each Wrong Option is Incorrect**
**Option A:** Odds ratio (OR) is a measure of association between an exposure and an outcome, but it is not the same as relative risk. OR is calculated differently and is used in case-control studies to estimate the strength of association between a risk factor and an outcome.
**Option B:** Absolute risk (AR) refers to the probability of an event or outcome occurring in a specific population or group. While AR is an important measure, it is not the same as relative risk, which compares the risk between two groups.
**Option C:** Attributable risk (AR) is a measure of the proportion of cases that can be attributed to a specific risk factor. While AR is related to relative risk, it is not the same measure.

**Clinical Pearl / High-Yield Fact**
Remember that relative risk is a useful measure for assessing the strength of association between a risk factor and an outcome, but it has limitations. For example, relative risk is sensitive to the baseline risk of the outcome in the non-exposed group, and it may not accurately reflect the risk in populations with very low or very high baseline risks.

**Correct Answer: D. Case-control study. Case-control study.**