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
Epidemiological study with population as a unit of study- 
Select and explain. 
A. Ecological study, B. Cohort study, C. Case reference study, D. Experimental study
A: Ecological study
Answer: A: Ecological study 
Explanation: Ans. 'a' i.e., Ecological study * Ecological study is an epidemiological study in which the unit of analysis is a population rather than an individual.* Therefore, ecological study utilizes data at the population level rather than the individual level. StudyUnit of study1.Observational studies A) Descriptive studies (formation of hypothesis) i) Case reportsii) Case series B) Analytic studies (testing of hypothesis) i) Case - control or case - referenceii) Cohort or follow-upiii) Ecological or correlational studyiv) Cross-sectional or pravalence studyIndividualsIndividualsPopulationIndividuals2.Experimental / intervention studies (testing of hvpothesis) i) Randamized controlled / clinical trialsii) Field trials or community intervention studiesiii) Community trialsiv) Animal studiesPatientsHealthy peopleCommunities