Morbidity and mortality rates

Morbidity and mortality rates

The analysis of morbidity and mortality caused by acute and chronic diseases forms the basis of many epidemiological studies. Morbidity represents the illness, symptoms, or impairments produced by a disease, whereas mortality is death caused by a disease. Acute diseases are those that strike and disappear quickly, within a month or so (e.g., chickenpox and influenza). Chronic diseases are those that are long-term; chronic diseases often are incurable (e.g., many forms of cancer and diabetes mellitus).
Morbidity and mortality rates allow researchers to compare disease cases and deaths to the unit size of population. A rate is a special type of proportion that includes a specification of time, and the numerator of the proportion is included in the denominator. Rates can be expressed in any form that is convenient (e.g., per 1,000, per 10,000, or per 100,000). Infant mortality rates, for example, are typically expressed per 1,000 live births, whereas cancer rates are expressed per 100,000 population.