Incidence of diarrhoea in a community can be calculated by-
Case control study
Coho study
Cross sectional study
Double blind placebo control study
Coho study is also known as incidence study. The cohos are identified prior to the appearance of disease under investigation. The study group so defined are observed over a period of time to determine the frequency of disease among them. (refer pgno:75 park 23rd edition)
Epidemiology