A study of distribution of disease among the population is known as epidemiology. This generally helps in the study of the entire evidence-based study and helps to the know the risk factor of the diseases. This study has a special techniques of data collection in terms of a subject. More often this can be done on a study sample of a selected sample of population. The terms such as mortality rate incidence and prevalence rate are mostly used in the case of epidemiology. This condition is mostly seen in the developing and under developed countries when compared to the developed countries due to lack of hygiene and spread of diseases.