A public health researcher in Delhi wants to investigate the association between occupational dust exposure and chronic obstructive pulmonary disease (COPD) among construction workers. The researcher has identified 150 workers with COPD and 150 age-matched workers without COPD, and will collect detailed occupational history from both groups. Which study design is most appropriate for this investigation?

Explanation

## Study Design Selection for Occupational Exposure Investigation ### Why Case-Control is Optimal Here **Key Point:** The researcher has already identified cases (COPD workers) and controls (non-COPD workers) and will retrospectively assess past exposure — this is the defining structure of a case-control study. **High-Yield:** Case-control studies are the investigation of choice when: - The outcome (disease) is already present at study entry - The exposure occurred in the past - The disease is relatively rare or has a long latency period - You need rapid, cost-effective data collection ### Comparison of Study Designs | Feature | Case-Control | Prospective Cohort | RCT | Cross-Sectional | |---------|--------------|-------------------|-----|------------------| | **Timing of exposure assessment** | Retrospective | Prospective | Prospective | Current | | **Suitable for occupational exposure?** | Yes (past exposure) | Yes (future exposure) | No (unethical to assign) | No (cannot establish causality) | | **Time to results** | Months | Years to decades | Years | Weeks | | **Cost** | Low to moderate | High | Very high | Low | | **Measures odds ratio** | Yes (directly) | No (calculates RR) | Yes (RR) | No (PR) | **Clinical Pearl:** In occupational epidemiology, case-control studies are preferred for investigating past exposures because workers with COPD can recall their dust exposure history, and the study can be completed in a reasonable timeframe without waiting for disease development. **Mnemonic: ROPE** — Remember Occupational Past Exposures = case-control design ### Why This Question Tests Study Design Mastery The stem explicitly states: - Cases and controls are **already identified** (not recruited prospectively) - Assessment will be of **past exposure** (retrospective) - The disease (COPD) is the **starting point** (not the endpoint) These three features lock in case-control as the answer.