Epidemiology is the branch of medical science devoted to the study of the distribution and determinants of diseases in populations. Descriptive and analytic epidemiology are observational, whereas clinical epidemiology is experimental in nature. Descriptive epidemiology is used to identify populations at an increased or decreased risk of disease or death, while analytic epidemiology is used to identify risk or protective factors for diseases.
Descriptive studies include the collection of data, analysis and dissemination of findings on disease incidence (new cases), prevalence, morbidity, survival and mortality. Analytic studies include case-control studies that compare individuals who have a disease with those who don't regarding their exposure to some potentially hazardous agent, and cohort studies, in which the disease experience of individuals exposed to an agent is compared with that of an unexposed population. Experimental epidemiology is restricted to the conduct of clinical trials.
Graduate school programs in epidemiology are offered at 10 Canadian universities: the universities of Alberta, Manitoba, British Columbia, Western Ontario, Toronto and Ottawa, and McGill University, Queen's University, Dalhousie University and McMaster University. Only two, McGill University and the University of Toronto, have long-standing PhD programs; other schools offer Master's degrees. Epidemiology programs are usually located within schools of Public Health or Community Medicine, and are often associated with biostatistics programs. Although there are no undergraduate programs in epidemiology, courses are offered as part of some undergraduate health sciences programs. Graduate students in epidemiology typically have an educational background in biology, statistics, medicine, nursing or social sciences.
Epidemiologic research is conducted by universities, governments and private industry. Federal and provincial governments (including provincial cancer agencies) are involved in disease surveillance and risk factor identification, whereas local health departments typically focus on disease surveillance and health promotion. The pharmaceutical industry conducts clinical trials to test the effectiveness of new therapeutic agents.
Until the 1960s most epidemiologic research focused on infectious disease outbreaks. The increasing importance of chronic diseases, coupled with methodologic advances, has led to a substantial increase in epidemiologic studies of chronic diseases such as cancer and heart disease. These studies have highlighted the importance of lifestyle factors such as cigarette smoking and diet in the etiology of these diseases. The advent of AIDS and the resurgence of "old" diseases such as tuberculosis has resulted in a renewed interest in infectious disease epidemiology.