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Biostatistics and Epidemiology Flashcards

7 cards from real NBME practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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

    Answer: Odds ratio

    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.

  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?

    Answer: 5 years

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

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

    Answer: Randomized controlled trial

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

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

    Answer: Hospital-based case-control studies

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

  5. The attack rate during an outbreak investigation is calculated as:

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

    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.

  6. A researcher enrolls 500 healthy adults and follows them for 10 years to track development of cardiovascular disease. This study design is:

    Answer: Prospective cohort study

    Enrolling disease-free participants at baseline and following them forward in time to observe new outcomes defines a prospective cohort study.

  7. Confounding in an epidemiological study occurs when:

    Answer: A third variable is associated with both the exposure and the outcome but is not on the causal pathway

    A confounder must be associated with the exposure, associated with the outcome, and not be an intermediate step between them; it creates a spurious or distorted association.