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
Natural history of a disease is studied with 
Select and explain. 
A. Longitudinal studies, B. Cross sectional studies, C. Randomized control trials, D. Randomized sampling
A: Longitudinal studies
Answer: A: Longitudinal studies 
Explanation: Longitudinal studies are in which observations are repeated in the same population over a prolonged period of time by means of follow-up examination. They are useful in1) to study the natural history of the disease and its future outcome2) for identifying risk factors for disease3) For finding out incidence rate or rate of occurrence of new cases of a disease in the community.Park 23e pg: 70