Comparative observational studies – cross-sectional, case-control, cohort MCQs With Answer

Comparative observational studies are essential in pharmacoepidemiology and clinical research for B.Pharm students. This concise guide introduces cross-sectional, case-control, and cohort designs, highlighting key concepts like incidence versus prevalence, temporality, exposure and outcome assessment, measures of association (odds ratio, relative risk), and common biases and confounding. Understanding strengths, limitations, prospective versus retrospective approaches, matching, and analytic strategies enables sound interpretation of real-world drug safety and effectiveness data. These observational methods underpin many pharmacy decisions, from adverse event surveillance to comparative effectiveness. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary purpose of a cross-sectional study?

• To measure incidence of a disease over time
• To assess prevalence of exposure and outcome at a single point in time
• To establish causality between exposure and outcome
• To follow a cohort prospectively for outcome development

Correct Answer: To assess prevalence of exposure and outcome at a single point in time

Q2. Which measure of association is most appropriate in a case-control study?

• Relative risk
• Risk difference
• Odds ratio
• Incidence rate ratio

Correct Answer: Odds ratio

Q3. In a prospective cohort study, which characteristic is true?

• Exposure and outcome are measured at the same time
• Exposure is measured before outcome occurs
• Participants are selected based on outcome status
• Only prevalence can be estimated

Correct Answer: Exposure is measured before outcome occurs

Q4. Which bias is most commonly associated with retrospective case-control studies?

• Loss to follow-up bias
• Recall bias
• Observer-expectancy bias
• Hawthorne effect

Correct Answer: Recall bias

Q5. Which observational design is most efficient for studying rare diseases?

• Cross-sectional study
• Case-control study
• Prospective cohort study
• Randomized controlled trial

Correct Answer: Case-control study

Q6. Which statement correctly contrasts incidence and prevalence?

• Prevalence measures new cases; incidence measures all existing cases
• Incidence measures new cases over time; prevalence measures total cases at a point or period
• Prevalence can only be used in cohort studies; incidence only in cross-sectional studies
• Incidence equals prevalence multiplied by study size

Correct Answer: Incidence measures new cases over time; prevalence measures total cases at a point or period

Q7. What does an odds ratio (OR) of 1.0 indicate in a case-control study?

• Exposure is protective against the outcome
• No association between exposure and outcome
• Exposure causes the outcome
• Study is biased and invalid

Correct Answer: No association between exposure and outcome

Q8. Matching in case-control studies is primarily used to:

• Increase sample size
• Control confounding by design
• Eliminate recall bias
• Convert a retrospective into a prospective study

Correct Answer: Control confounding by design

Q9. A nested case-control study is best described as:

• A case-control study performed within a defined cohort
• A cross-sectional survey followed by randomization
• A series of case reports linked by exposure
• A meta-analysis of cohort studies

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

Q10. Which analytic method helps control for multiple confounders in observational studies?

• Student’s t-test
• Stratified analysis and multivariable regression
• Simple proportion comparison
• Kaplan-Meier curve without modeling

Correct Answer: Stratified analysis and multivariable regression

Q11. Which limitation is most associated with cross-sectional studies when assessing causality?

• High cost and long follow-up
• Temporal ambiguity between exposure and outcome
• Difficulty measuring prevalence
• Inability to include controls

Correct Answer: Temporal ambiguity between exposure and outcome

Q12. Relative risk (risk ratio) can be directly calculated in which study design?

• Case-control study
• Cross-sectional study only
• Cohort study
• Systematic review only

Correct Answer: Cohort study

Q13. Which is a major strength of cohort studies for pharmacoepidemiology?

• Low cost with immediate results
• Ability to assess multiple outcomes from a single exposure
• No risk of confounding
• Guaranteed absence of selection bias

Correct Answer: Ability to assess multiple outcomes from a single exposure

Q14. In a case-control study, controls should ideally be selected from:

• The general population with similar exposure distribution as cases would have had
• Only healthy people with no disease history
• Patients from a different hospital unrelated to cases
• Individuals with the outcome of interest

Correct Answer: The general population with similar exposure distribution as cases would have had

Q15. Which bias arises when loss to follow-up differs between exposed and unexposed groups in cohort studies?

• Information bias
• Selection bias (attrition bias)
• Publication bias
• Confounding by indication

Correct Answer: Selection bias (attrition bias)

Q16. Confounding by indication is particularly relevant in which context?

• Randomized controlled trials only
• Observational drug effectiveness or safety studies
• Laboratory animal experiments
• Cross-sectional surveys asking only demographics

Correct Answer: Observational drug effectiveness or safety studies

Q17. Which approach best assesses effect modification (interaction) in observational data?

• Ignore subgroup differences and present overall estimate
• Test interaction terms in a regression model and stratified analysis
• Only use univariate tests for each covariate
• Match cases and controls on the effect modifier

Correct Answer: Test interaction terms in a regression model and stratified analysis

Q18. In pharmacoepidemiology, a prospective cohort is preferred over retrospective because:

• It always costs less
• Exposure measurement can be more accurate and standardized before outcome
• It eliminates all biases automatically
• It requires no ethical approval

Correct Answer: Exposure measurement can be more accurate and standardized before outcome

Q19. Which measure is most appropriate to estimate the public health burden from a cross-sectional study?

• Incidence rate
• Prevalence proportion
• Odds ratio for rare outcomes only
• Hazard ratio

Correct Answer: Prevalence proportion

Q20. Case-control studies are prone to selection bias when:

• Controls are selected independently of exposure status
• Controls are chosen from a source population that differs in exposure opportunities from cases
• Cases and controls are matched on confounders
• Exposure is measured objectively from records

Correct Answer: Controls are chosen from a source population that differs in exposure opportunities from cases

Q21. Which statement about incidence density sampling in nested case-control studies is correct?

• Controls are selected only at baseline and never again
• Controls can be sampled at the time each case occurs, allowing control exposure distribution to reflect person-time
• It estimates prevalence rather than incidence
• It requires matching on outcome status

Correct Answer: Controls can be sampled at the time each case occurs, allowing control exposure distribution to reflect person-time

Q22. Information bias in observational studies typically refers to:

• Systematic differences in how exposure or outcome data are measured or classified
• Differences in baseline characteristics between study groups
• Random variation due to small sample size
• Bias introduced by publishing only positive results

Correct Answer: Systematic differences in how exposure or outcome data are measured or classified

Q23. Which analytic strategy can help address unmeasured confounding in observational studies?

• Standard logistic regression with measured covariates only
• Instrumental variable analysis
• Simple cross-tabulation without adjustment
• Increasing sample size alone

Correct Answer: Instrumental variable analysis

Q24. Which design allows calculation of both incidence and multiple exposures’ effects when exposure is rare?

• Cross-sectional study
• Prospective cohort with oversampling of exposed individuals
• Case series without controls
• Traditional case-control without exposure data

Correct Answer: Prospective cohort with oversampling of exposed individuals

Q25. When interpreting an odds ratio from a case-control study, under what condition is OR a good approximation of relative risk?

• When the outcome is rare in the source population
• When the exposure prevalence is >50%
• When matching is not used
• When sample size is extremely large regardless of outcome frequency

Correct Answer: When the outcome is rare in the source population

Q26. What is the main disadvantage of cross-sectional studies for evaluating drug adverse effects?

• They are expensive and time-consuming
• They cannot establish temporal sequence between drug exposure and adverse effect
• They always require randomization
• They overestimate incidence by design

Correct Answer: They cannot establish temporal sequence between drug exposure and adverse effect

Q27. Which criterion is essential to consider when selecting controls in a hospital-based case-control study?

• Controls should have the exposure of interest more often than cases
• Controls should be selected from patients with diseases unrelated to the exposure under study
• Controls must have the same outcome as cases
• Controls must be younger than cases

Correct Answer: Controls should be selected from patients with diseases unrelated to the exposure under study

Q28. Attrition in a long-term cohort study can lead to biased results if:

• Dropout is completely random and unrelated to exposure or outcome
• Loss to follow-up is related to both exposure and outcome
• Only baseline data are analyzed
• All participants are followed until the study end

Correct Answer: Loss to follow-up is related to both exposure and outcome

Q29. Which of the following best describes confounding?

• A variable that lies on the causal pathway between exposure and outcome
• An extraneous factor associated with both exposure and outcome that distorts their association
• A random error due to measurement imprecision
• A bias introduced by selective publication

Correct Answer: An extraneous factor associated with both exposure and outcome that distorts their association

Q30. For assessing temporal changes in drug safety signals, which study design is most informative?

• Cross-sectional survey at one time point
• Repeated or longitudinal cohort studies tracking incidence over time
• Case reports without denominator data
• Single case-control study with retrospective exposure ascertainment

Correct Answer: Repeated or longitudinal cohort studies tracking incidence over time

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