A measure of the death rate in a biological population, usually presented in terms of the number of deaths per hundred or per thousand. If there are 100 mice at the beginning of the year and fifteen of them die by the end of the year, the group's mortality rate is fifteen per 100 individuals (the initial population), or 15 percent. In ecological and demographic studies of populations mortality is an important measurement, along with birth rates (natality), immigration, and emigration, used to assess changes in population size over time. In human populations mortality rates are often figured for specific age and gender groups, or for other population categories including race, income level, occupation, and so on. This way group mortality rates can be compared and risks for each subgroup can be evaluated.

See Also

Evolution; Extinction; Population Growth; Zero Population Growth