<prompt> Following is true about longitudinal studiesUsed to study the natural history of the diseaseSingle outcomeAre economicalAre efficient  <response>: Longitudinal studies are useful in: To study the natural history of disease and its future outcome For identifying risk factors of disease For finding out incidence rate or rate of occurrence of new cases of disease in the community Ref: 25th edition, Parks Textbook of Preventive and Social Medicine, Page no. 78 