Which of the following is a major disadvantage of case-control studies compared to cohort studies?

Explanation

## Temporal Relationship in Case-Control vs Cohort Studies ### The Critical Difference **Key Point:** Case-control studies are **retrospective** — they start with disease (cases and controls) and look **backward** to assess prior exposure. This makes it difficult to establish that exposure **preceded** disease onset, which is essential for causation. ### Why Temporal Relationship is Compromised | Aspect | Cohort Study | Case-Control Study | |--------|--------------|--------------------| | **Direction** | Forward (prospective) | Backward (retrospective) | | **Temporal sequence** | Exposure → Disease (clear) | Disease ← Exposure (unclear) | | **Causation criterion** | Can establish | Difficult to establish | | **Recall bias** | Minimal (exposure measured at baseline) | High (subjects recall past exposure) | **High-Yield:** The **temporal sequence** (exposure before disease) is a fundamental criterion for establishing causation. Case-control studies struggle with this because: 1. Disease has already occurred when study begins 2. Exposure status is determined retrospectively (often from memory) 3. Cannot rule out reverse causation (disease causing the exposure) ### Example In a case-control study of lung cancer and smoking: - Cases (lung cancer patients) report past smoking history - But did they smoke **before** or **after** diagnosis? - Recall bias: sick patients may over-report exposure **Clinical Pearl:** Case-control studies excel at studying **rare diseases** (efficient) but are inherently weaker at proving causation due to temporal ambiguity. [cite:Park 26e Ch 9]