A public health researcher in Delhi is investigating the association between occupational dust exposure and chronic obstructive pulmonary disease (COPD) among construction workers. The researcher identifies 500 construction workers with COPD diagnosed in the past 2 years and 500 age-matched construction workers without COPD. Both groups are then questioned about their past dust exposure history over the preceding 10 years. Which study design is being employed, and what is the primary limitation of this approach in establishing causality?

Explanation

## Study Design Identification **Key Point:** This is a **case-control study** because the researcher starts with disease status (COPD present vs. absent) and then looks backward in time to ascertain exposure history. ## Primary Limitation: Recall Bias **High-Yield:** In case-control studies, recall bias is a critical threat to validity because: 1. **Cases (COPD patients)** may over-report past dust exposure because they attribute their disease to occupational factors. 2. **Controls (non-COPD workers)** may under-report exposure because they have no disease to motivate recall. 3. This differential recall distorts the exposure-disease association, potentially inflating or deflating the odds ratio. ## Why Case-Control is Chosen Here - COPD has a long latency period (10+ years); a prospective cohort would be impractical. - Cases are already identified (prevalent cases), making case-control efficient and cost-effective. - The study is retrospective, asking about past exposure. ## Comparison: Recall Bias vs. Other Biases | Bias Type | Mechanism | Why Not the Answer | |-----------|-----------|-------------------| | **Recall bias** | Differential memory of exposure by disease status | **CORRECT** — the primary limitation here | | Selection bias | Differential inclusion of cases/controls by exposure | Present but not the primary limitation in this scenario | | Confounding | Unmeasured third variables | Can be addressed by matching or stratification | **Clinical Pearl:** Recall bias is especially problematic in occupational epidemiology because workers with disease are motivated to remember exposures, while healthy controls may not recall minor dust exposure events. **Mnemonic: REC** — **Recall bias in case-control studies is Exposure-related and Contingent on disease status.**