This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Analytical Epidemiology, Subject name: Social & Preventive Medicine
Natural history of disease can be studied by - 
Select and explain. 
A. Cross sectional study, B. Ecological study, C. Cohort study, D. RCT
C: Cohort study
Answer: C: Cohort study 
Explanation: Ans. is 'c' i.e., Cohort study o Longitudinal studies are used to study natural history of disease. Among the given options, only cohort study is a longitudinal study.Longitudinal studieso In this type ofstudy observations are repeated in the same population over a prolonged period of time by means of follow up examinations.o They are useful toStudy the natural history of diseaseFor identifying risk factors of diseaseFor finding out incidence rate or rate of recurrence of new cases of disease.Note : Longitudinal studies are difficult to organize and more time consuming than cross sectional studies