NBME Biostatistics and Epidemiology 2

Question 1

Which measure of association is used in a case-control study?

Accepted Answer

Odds ratio

Answer

Because case-control studies start with outcome status (not exposure), incidence cannot be calculated directly; the odds ratio is used as an approximation of relative risk.

Question 2

A disease has a prevalence of 50 per 1,000 and an incidence of 10 per 1,000 per year. What is the average disease duration?

Accepted Answer

5 years

Answer

Using the steady-state formula Prevalence = Incidence × Duration: Duration = 50/10 = 5 years.

Question 3

Which study design provides the STRONGEST evidence for a causal relationship between an exposure and outcome?

Accepted Answer

Randomized controlled trial

Answer

Randomized controlled trials eliminate confounding through random assignment, providing the highest level of evidence for causality.

Question 4

Berkson's bias is a specific type of selection bias most likely to occur in:

Accepted Answer

Hospital-based case-control studies

Answer

Berkson's bias arises when hospitalized controls differ systematically from the general population, distorting the exposure-disease association in hospital-based case-control studies.

Question 5

The attack rate during an outbreak investigation is calculated as:

Accepted Answer

(Number of new cases / Total population at risk) × 100

Answer

The attack rate equals the number of new cases divided by the total population at risk during a specified time period, expressed as a percentage.

NBME Practice Test

NBME Practice Test

NBME Biostatistics and Epidemiology 2