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What is All of the following are Experimental / Interventional studies except: and explain in detail?
Ecological study (Correlational study):

Type of analytical (observational) epidemiological study which provide the ‘least satisfactory type of evidence on causality’
Units of study: Population
Advantage: Data can be used from populations with different characteristics
Potential problem: Socio-economic confounding
Ecological fallacy: Is an error of interpretation of statistical data in an ecological study, whereby characteristics are ascribed to a group of individuals which they may not possess as individuals