In an ecological study evaluating sodium intake and hypertension prevalence across 20 countries, researchers find a strong positive correlation (r = 0.85). A researcher then concludes that individuals who eat more sodium have higher risk of hypertension. This logical error is called:
- A Selection bias
- B Ecological fallacy ✓
- C Confounding
- D Berkson's bias
Correct answer: B. Ecological fallacy
Explanation
Ecological fallacy (Robinson's paradox) occurs when group-level associations are incorrectly applied to individuals. Ecological studies use population-level data; the high sodium countries may also differ on other determinants of hypertension. Individual-level inference cannot be made from aggregate-level correlations. Selection bias involves non-representative samples. Confounding is a separate type of error at the individual level. Berkson's bias relates to hospital controls.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.