This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'All of the following are Experimental / Interventional studies except: \nSelect and explain. \nA. Randomised control trials ., B. Field trials., C. Community trials., D. Ecological studies.', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ecological study (Correlational study):\n\nType of analytical (observational) epidemiological study which provide the ‘least satisfactory type of evidence on causality’\nUnits of study: Population\nAdvantage: Data can be used from populations with different characteristics\nPotential problem: Socio-economic confounding\nEcological 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', 'role': 'assistant'}]