<prompt> By which of the following method the incidence of a disease can be calculated?Prospective studyRetrospective studyCase control studyCross sectional study  <response>: Prospective study is the exposure to the risk factor and subsequent health outcomes are observed after the beginning of the study. Incidence can be calculated by this study. Ref: Parks Textbook of Preventive and Social medicine, 19th edition, Page 71, 74. 