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
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: 
Select and explain. 
A. Ecological, B. Cross-sectional, C. Psephological study, D. Experimental study
A: Ecological
Answer: A: Ecological 
Explanation: Ans. a. Ecological