Observational study designs: cohort, case-control, cross-sectional MCQs With Answer

Introduction:

Observational study designs—cohort, case-control, and cross-sectional—are foundational tools in clinical research and pharmacovigilance. For M. Pharm students, understanding these designs is essential for evaluating drug safety, identifying risk factors, and interpreting real-world evidence. Cohort studies measure incidence and can establish temporality; case-control studies are efficient for rare outcomes and use odds ratios; cross-sectional studies assess prevalence and generate hypotheses. This quiz collection presents focused MCQs that deepen comprehension of study selection, measures of association, sampling strategies, biases, confounding, and analytic approaches commonly used in observational research. Practicing these questions will strengthen critical appraisal skills required in advanced pharmacovigilance and clinical research.

Q1. Which observational design follows exposed and unexposed groups forward in time to compare incidence of outcomes?

• Cohort study
• Case-control study
• Cross-sectional study
• Ecological study

Correct Answer: Cohort study

Q2. Which study design selects participants based on outcome status and retrospectively assesses prior exposures?

• Cohort study
• Case-control study
• Cross-sectional study
• Randomized controlled trial

Correct Answer: Case-control study

Q3. Which design primarily provides a snapshot estimate of disease prevalence at a single point in time?

• Prospective cohort study
• Case-control study
• Cross-sectional study
• Nested case-control study

Correct Answer: Cross-sectional study

Q4. What is the preferred measure of association estimated directly in a cohort study comparing cumulative incidences?

• Odds ratio
• Relative risk (risk ratio)
• Prevalence ratio
• Attributable fraction

Correct Answer: Relative risk (risk ratio)

Q5. What measure of association is most commonly used in case-control studies?

• Risk difference
• Incidence rate ratio
• Odds ratio
• Hazard ratio

Correct Answer: Odds ratio

Q6. For investigating a rare disease with limited resources, which observational design is usually most efficient?

• Prospective cohort study
• Case-control study
• Cross-sectional study
• Ecological time-trend study

Correct Answer: Case-control study

Q7. Which study approach uses person-time denominators to calculate incidence rates?

• Cross-sectional study
• Case-control study
• Cohort study
• Ecological study

Correct Answer: Cohort study

Q8. A nested case-control study is best described as which of the following?

• A case-control study nested within a defined cohort
• A cross-sectional survey repeated over time
• An ecological comparison across regions
• A randomized sampling of cases without controls

Correct Answer: A case-control study nested within a defined cohort

Q9. Matching in case-control studies is used primarily to:

• Increase sample size
• Eliminate all bias
• Reduce confounding by equalizing matched variables between cases and controls
• Convert a retrospective design into a prospective one

Correct Answer: Reduce confounding by equalizing matched variables between cases and controls

Q10. Which type of bias is particularly a concern in case-control studies relying on participant recall of past exposures?

• Selection bias
• Confounding bias
• Recall (information) bias
• Observer-expectancy bias

Correct Answer: Recall (information) bias

Q11. High loss to follow-up in a prospective cohort study threatens validity mainly through:

• Random error
• Attrition bias leading to selection bias and potential confounding
• Improved generalizability
• Increased incidence rates automatically

Correct Answer: Attrition bias leading to selection bias and potential confounding

Q12. Which sampling approach selects controls who are at risk at the time each case occurs, often used in nested case-control studies?

• Case-cohort sampling
• Incidence density (risk-set) sampling
• Simple random sampling of the entire cohort at baseline
• Cross-sectional sampling

Correct Answer: Incidence density (risk-set) sampling

Q13. Which study design can directly estimate disease incidence?

• Case-control study
• Cohort study
• Cross-sectional study
• Ecological study

Correct Answer: Cohort study

Q14. Under what condition does the odds ratio from a case-control study approximate the relative risk?

• When exposure is rare
• When outcome is rare
• Only when matching is used
• When the sample size is small

Correct Answer: When outcome is rare

Q15. Which observational design is typically quickest and least expensive to conduct for assessing associations at a single time point?

• Prospective cohort study
• Case-control study
• Cross-sectional study
• Longitudinal panel study

Correct Answer: Cross-sectional study

Q16. A case-cohort study differs from a nested case-control study mainly because:

• Controls are selected as a random subcohort at baseline and can serve multiple outcomes
• It only includes incident cases and no controls
• It samples controls only after each case event
• It is identical to cross-sectional sampling

Correct Answer: Controls are selected as a random subcohort at baseline and can serve multiple outcomes

Q17. Which design best ensures temporality between exposure and outcome for causal inference?

• Cross-sectional study
• Case-control study
• Prospective cohort study
• Ecological study

Correct Answer: Prospective cohort study

Q18. Selecting controls from a hospital population when cases are community-based is an example of which problem?

• Information bias
• Selection bias
• Confounding by indication
• Measurement bias

Correct Answer: Selection bias

Q19. Which measure is obtained from survival analysis (e.g., Cox proportional hazards model) and compares time-to-event between groups?

• Odds ratio
• Risk difference
• Hazard ratio
• Prevalence ratio

Correct Answer: Hazard ratio

Q20. In observational studies, which analytic method is commonly used to adjust simultaneously for multiple confounders?

• Randomization
• Stratified crude analysis
• Matching only
• Multivariable regression (e.g., logistic or Cox regression)

Correct Answer: Multivariable regression (e.g., logistic or Cox regression)

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