American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the standard outcome measure for a cohort study?

1. Absolute risk

2. Prevalence

3. Relative risk

4. Odds ratio

The correct answer is: Relative risk

In a cohort study, the standard outcome measure used to evaluate the association between exposure and the occurrence of an outcome is relative risk. Relative risk quantifies how much more (or less) likely an outcome is to occur in the exposed group compared to the unexposed group. This measure provides clear insight into the strength of the association and helps in understanding the potential impact of the exposure on the outcome. Relative risk is particularly useful because it directly addresses the question of how exposure alters the likelihood of an event happening. It is calculated by dividing the incidence rate of the outcome in the exposed group by the incidence rate of the outcome in the unexposed group. This approach is foundational in epidemiology and allows researchers to draw conclusions about causation and risk related to exposures over time. The ability to interpret relative risk is critical for public health recommendations and clinical decision-making. In contrast, while absolute risk gives an individual estimate of risk, it does not provide a comparative measure of risk between exposed and unexposed groups. Prevalence measures the proportion of a population with a particular condition at a specific time, which does not reflect the temporal relationship studied in cohort designs. Odds ratio is another measure used in case-control studies and logistic regression, but it isn't