Epidemiology is the branch of medical science that investigates all the factors that determine the presence or absence of diseases and disorders. that deals with the study of the causes, distribution, and control of disease in populations. Much of the data that epidemiologists collect comes from self-report” from answers provided by people participating in a study. The impact factor of journal provides quantitative assessment tool for grading, evaluating, sorting and comparing journals of similar kind. It reflects the average number of citations to recent articles published in science and social science journals in a particular year or period, and is frequently used as a proxy for the relative importance of a journal within its field. It is first devised by Eugene Garfield, the founder of the Institute for Scientific Information. The impact factor of a journal is evaluated by dividing the number of current year citations to the source items published in that journal during the previous two years.