Evidence-appraisal glossary
Ecological fallacy
The ecological fallacy is the error of assuming that a relationship seen in group-level averages also holds for the individuals within those groups. A correlation between two things across countries or regions does not mean the same two things are linked in any one person.
Also called: ecological inference fallacy.
Ecological studies compare aggregated data, such as average salt intake and average blood pressure across nations, which is convenient but can mislead because group averages hide how the variables are distributed within each group. A classic case is finding that regions with more immigrants have higher literacy, which need not mean immigrants themselves are more literate. The fallacy is a reason to be cautious drawing conclusions about individuals from population statistics, though ecological data can still be useful for generating hypotheses and studying genuinely group-level exposures.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.