Definition of epidemiology
The study of the occurrence and distribution of health-related states or events in specified populations, including the study of the determinants influencing such states, and the application of this knowledge to control health problems.
The primary "knowledge object" of epidemiology as a scientific discipline is causes of health-related events in populations. In the past 70 years, the definition has broadened from concern with communicable disease epidemics to take all processes and phenomena related to health in populations. Therefore epidemiology is much more than a branch of medicine treating epidemics.
International Epidemiological Association. A Dictionary of Epidemiology (ed. Porta M). Oxford: Oxford University Press, 5th edition, 2008
Study involves surveillance, observation, hypothesis testing, analytic research, and experiments
Distribution refers to the analysis by time, place, and classes or subgroups of persons affected in a population or in a society
Determinants are all the physical, biological, social, cultural, economic, and behavioural factors that influence health
Health-related states and events include diseases, causes of death, behaviours, reactions to preventive programmes, and provision and use of health services
Specified populations are those with common identifiable characteristics
Application to control ... makes explicit the aim of epidemiology: