Epidemiology is the study of how often disease occurs in different groups of people and why.
Epidemiology seeks to describe the frequency of disease and it's distribution in terms of person, place and time factors.
Epidemiology seeks to assess determinants or possible causes of disease in terms of host, agent and environment.
Most epidemiological investigations of aetiology are observational. They look for associations between the occurrence of disease and exposure to known or suspected causes.
Information needed in an epidemiologic study are;
Identification of study population
The size of the population
The type of population
The number of person affected with disease
Cause agent of the disease
How it can be controlled