This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Social & Preventive Medicine
Study unit of ecological study is 
Select and explain. 
A. Population, B. Patient, C. Community, D. Case
A: Population
Answer: A: Population 
Explanation: In ecological studies the unit of observation is the population or community. * Disease rates and exposures are measured in each of a series of populations and their relation is examined. * Often the information about disease and exposure is abstracted from published statistics and therefore does not require expensive or time