A researcher is designing a study to investigate the association between occupational asbestos exposure and lung cancer in Indian factory workers. Regarding the characteristics of case-control studies, all of the following statements are correct EXCEPT:

Explanation

## Temporal Relationship in Case-Control Studies ### Why Option 2 is Incorrect (The Exception) **Key Point:** Although case-control studies are typically retrospective in design, they CAN and DO establish temporal relationship between exposure and disease. The temporal sequence is established by the LOGIC of the study design, not by the direction of data collection. **High-Yield:** In a case-control study: 1. Cases have the disease (outcome already occurred) 2. Controls do not have the disease 3. Both groups are asked about past exposure 4. By definition, exposure must have occurred BEFORE disease diagnosis Therefore, temporal precedence is inherent to the case-control design — it is logically established even though data collection is retrospective. ### Why the Other Options are Correct | Statement | Validity | Explanation | |-----------|----------|-------------| | Option 0: OR ≈ RR when disease is rare | ✓ Correct | When prevalence < 10%, OR approximates RR; useful for interpreting case-control results | | Option 1: Independent selection | ✓ Correct | Cases and controls must be selected based on disease status alone, not exposure; otherwise selection bias occurs | | Option 3: Cost & time advantage | ✓ Correct | Retrospective design is faster and cheaper than prospective cohort, ideal for rare outcomes like occupational cancers | ### Clinical Pearl **Temporal Relationship in Occupational Studies:** In asbestos-lung cancer case-control studies, temporal relationship is automatically established because: - Cases have lung cancer (diagnosed at study entry) - Exposure history is collected retrospectively - Exposure logically preceded diagnosis by years or decades This is why case-control studies are the gold standard for occupational and environmental epidemiology in India, despite being retrospective. ### Common Misconception ~~"Case-control studies cannot establish temporal relationship because they are retrospective."~~ **Correct understanding:** Temporal relationship is established by the inherent logic of the design (disease → exposure history), not by the direction of data collection. Retrospective data collection does not negate temporal precedence. [cite:Park 26e Ch 8]