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
False about longitudinal studies is - 
Select and explain. 
A. Identifies risk factor, B. Used to study natural history of disease, C. Incidence can't be measured, D. All
C: Incidence can't be measured
Answer: C: Incidence can't be measured 
Explanation: .longitudinal studies are those studies in which observations are repeated in the same population over a prolonged period of time by means of follow-up examinations.longitudinal studies can be likened to a cine film.they are useful in, 1.to study the natural history of a disease and its future outcome. 2.for identifying risk factors of disease. 3.for finding out the incidence rate or rate of occurrence of new cases .these studies are difficult to organise and more time consuming than cross-sectional studies. ref:park&;s textbook,ed 22,pg no 66