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What Is Epidemiology?

Epidemiology is the branch of medical science that investigates all the factors that determine the presence or absence of diseases and disorders. Epidemiological research helps us to understand how many people have a disease or disorder, if those numbers are changing, and how the disorder affects our society and our economy.

The epidemiology of human communication is a rewarding and challenging field. Much of the data that epidemiologists collect comes from self-report—from answers provided by people participating in a study. For instance, an epidemiological study may collect data on the number of people who answer, “Yes” when asked if someone in their household has trouble hearing. Each person providing such an answer may interpret “trouble hearing” differently. This means that the results of such a study may be quite different from a study in which actual hearing (audiometric) tests are administered to each person in a household.

Also, many epidemiological estimates try to determine how the number of people affected by a disorder changes over time. The definition of a disorder also tends to change over time, however, making estimates more difficult. Even scientists working in the same field at the same time may not agree on the best way to measure or define a particular disorder.

Key terms to know in this field are:

  • Incidence: The number of new cases of a disease or disorder in a population over a period of time.
  • Prevalence: The number of existing cases of a disease in a population at a given time.
  • Cost of illness: Many reports use expenditures on medical care (i.e., actual money spent) as the cost of illness. Ideally, the cost of illness would also take into account factors that are more difficult to measure, such as work-related costs, educational costs, the cost of support services required by the medical condition, and the amount individuals would pay to avoid health risks. (Adapted from the Environmental Protection Agency’s Cost of Illness Handbook)
  • Burden of disease: The total significance of disease for society, beyond the immediate cost of treatment. It is measured in years of life lost to ill health, or the difference between total life expectancy and disability-adjusted life expectancy (DALY). (Adapted from the World Health Organization.)
  • DALY (Disability-Adjusted Life Year): A summary measure of the health of a population. One DALY represents one lost year of healthy life and is used to estimate the gap between the current health of a population and an ideal situation in which everyone in that population would live into old age in full health. (Adapted from the World Health Organization.)

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