BHS Epidemiology 2 — Questions and Answers
Question 1: A study follows 500 smokers and 500 non-smokers for 10 years to compare lung cancer rates. What study design is this?
- Case-control study
- Prospective cohort study (Correct answer)
- Cross-sectional study
- Randomized controlled trial
Correct answer: Prospective cohort study
A prospective cohort study follows exposed and unexposed groups forward in time to measure disease incidence.
Question 2: The number of existing cases of a disease in a population at a specific point in time is called:
- Incidence rate
- Attack rate
- Point prevalence (Correct answer)
- Cumulative incidence
Correct answer: Point prevalence
Point prevalence measures all existing cases (new and old) at a single point in time.
Question 3: Which measure of association is most commonly reported in a cohort study?
- Odds ratio
- Prevalence ratio
- Relative risk (Correct answer)
- Attributable risk percent
Correct answer: Relative risk
Relative risk (risk ratio) compares incidence rates between exposed and unexposed groups and is directly calculable in cohort studies.
Question 4: Berkson's bias is a type of selection bias that occurs in:
- Community-based cohort studies
- Hospital-based case-control studies (Correct answer)
- Randomized trials
- Ecological studies
Correct answer: Hospital-based case-control studies
Berkson's bias arises when hospital controls have different exposure rates than the general population, distorting associations.
Question 5: An investigator finds that the association between coffee and pancreatic cancer disappears after adjusting for smoking. This illustrates:
- Effect modification
- Information bias
- Confounding by smoking (Correct answer)
- Reverse causality
Correct answer: Confounding by smoking
When an apparent association is explained by a third variable related to both exposure and outcome, confounding is present.
Question 6: Which of the following best describes the 'attack rate' used during an outbreak investigation?
- The proportion of exposed individuals who develop the disease (Correct answer)
- The rate of new cases per 100,000 person-years
- The ratio of cases to deaths
- The number of secondary cases per primary case
Correct answer: The proportion of exposed individuals who develop the disease
Attack rate is the proportion of a defined population (usually exposed) that develops illness during a specified period.
Question 7: In an epidemic curve showing a single sharp peak followed by rapid decline, what pattern of transmission is most likely?
- Propagated person-to-person spread
- Common-source continuous exposure
- Point-source common-source outbreak (Correct answer)
- Vector-borne transmission
Correct answer: Point-source common-source outbreak
A narrow, single-peaked epidemic curve suggests a point-source exposure where most cases occur within one incubation period.
BHS Epidemiology 2
A study follows 500 smokers and 500 non-smokers for 10 years to compare lung cancer rates.
What study design is this?