An investigator finds that districts with higher female literacy rates report more hospital deliveries, and concludes that educating women makes them less likely to deliver at home. On checking individual-level survey data, educated and uneducated women in the same district have nearly identical institutional delivery rates. The error the investigator has committed is best described as:

• A Selection bias
• B Ecological fallacy ✓
• C Information bias
• D Confounding by district wealth

Explanation

The ecological fallacy occurs when an association observed between variables at the group level is wrongly assumed to hold at the individual level. Districts with high literacy may also have better health infrastructure, so district-level correlation does not mean literate women themselves choose institutional delivery. Selection bias refers to systematic errors in how subjects are enrolled, information bias to misclassification of exposure or outcome, and confounding requires a third variable associated with both exposure and outcome within individuals.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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