Question

The ratio of the risk of disease among those exposed to a factor to the risk among those not exposed is defined as:

• A. Relative risk
• B. Odds ratio
• C. Attributable risk
• D. None of the above

Hint:

A ratio (not a difference) of incidence in exposed versus non-exposed.

Answer 1

The Correct Option is A

Step 1: Read the definition carefully - it is a division of one risk by another, specifically exposed risk over non-exposed risk. A ratio of two incidence rates points to the risk ratio, which is the relative risk. Step 2: Express it formally as $RR = \dfrac{P(\text{event} \mid \text{exposed})}{P(\text{event} \mid \text{not exposed})}$. Interpretation: a value of 1 indicates no link between exposure and disease, a value above 1 flags a harmful exposure, and a value below 1 flags a protective exposure. Step 3: Why not the others - the odds ratio divides odds rather than probabilities and is the natural estimate in case-control designs; attributable risk subtracts the non-exposed incidence from the exposed incidence to give the absolute excess, so it is a difference and not a ratio. Step 4: Since the stem describes a ratio of exposed to non-exposed risk, the correct measure is the relative risk. \[\boxed{\text{Relative risk}}\]