This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
[{'content': 'Study unit of ecological study is: \nSelect and explain. \nA. Population, B. Patient, C. Community, D. Case', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. a. PopulationRef: Park's Text book of Preventive and Social Medicine, 24th Ed; Page No-67There are 2 types of epidemiological studyObservational studyEcological study - population...unit of studyCross sectional study - individual...unit of studyCase-control study - individual...unit of studyChart study - individual...unit of studyExperimental studyRCT/Clinical trials - patients...unit of studyField trial - healthy population...unit of studyCommunity trial - communities...unit of study", 'role': 'assistant'}]