False about longitudinal studies is -

.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