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: Social & Preventive Medicine
[{'content': 'An investigator obtained an increased incidence of a disease due to low fiber diet in a country by obtaining data from the health authorities and food industry of the country. This type of study is known as: \nSelect and explain. \nA. Ecological, B. Cross-sectional, C. Psephological study, D. Experimental study', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. a. Ecological', 'role': 'assistant'}]