**Question:** Relative risk of a disease measures which of the following:

A. Increase in absolute risk
B. Reduction in absolute risk
C. Increase in odds ratio
D. Reduction in hazard ratio

**Core Concept:**
The concept of relative risk (RR) is important when assessing the impact of an exposure or intervention on the likelihood of an event. Relative risk compares the likelihood of an event occurring in a group exposed to a factor (case group) with the likelihood in a group not exposed to that factor (control group).

**Why the Correct Answer is Right:**
The correct answer, B. Reduction in absolute risk, refers to the change in the number of cases or events per unit of time or population. When assessing the impact of a factor on the incidence of a disease, understanding the absolute risk reduction can help determine the public health impact and guide decision-making.

**Why Each Wrong Option is Incorrect:**
A. Increase in absolute risk (Option A) focuses on the absolute number of cases or events, without considering the comparison to a control group. This option does not accurately represent the concept of relative risk.

C. Increase in odds ratio (Option C) is a measure of the relative strength of an association between an exposure and an outcome, while odds ratios do not directly provide information about the impact on disease incidence.

D. Reduction in hazard ratio (Option D) is a measure of the risk reduction in a population, often used in cancer research but not as relevant in assessing the impact of an exposure on disease incidence.

**Clinical Pearl:**
Understanding relative risk and absolute risk reduction allows for a comprehensive evaluation of the impact of a factor on disease incidence. This knowledge is essential for making informed decisions regarding public health interventions, clinical trials, and patient care.