mortality

mortality, mortality rate

The death-rate, usually standardized by age and sex, to facilitate comparisons between areas and social groups. It provides a measure of health risks, improvements in the quality of health care, and the comparative overall health of different groups in the population. It is thus used as a reliable indicator of social and economic change, and of comparative standards of living, as well as by epidemiologists who are interested in monitoring the risk of death from infectious diseases and other causes. A variety of mortality rates are used, each with its own purpose, with the overall national death-rate used as the starting-point for comparisons between areas and social groups in a society.

The crude death-rate is the number of deaths in a year per 1000 population in a defined geographical area. In effect a refined version of the absolute number of deaths, this is not very informative, as so much depends on the sex-ratio and age-structure of a population. Crude death-rates can be multiplied by Area Comparability Factors to produce corrected rates which are comparable one with another and enable direct comparisons between areas. More commonly, age-standardized death-rates are calculated separately for men and women, to produce overall Standard Mortality Ratios (SMR) for each sex, or for both sexes combined, for a given area or social group. The SMR compares age-specific death-rates for a given area or social group with national average age-specific death-rates. It is computed as the actual or observed number of deaths in the group of interest, divided by the expected number of deaths, multiplied by 100. (The expected number of deaths is the number that would have occurred if age-specific death-rates in the group of interest were equal to the national averages for the year.) Age-specific crude death-rates and SMRs can also be calculated to identify the age-groups accounting for mortality rates above or below the national average. Five-year and ten-year age-bands are normally used, but broader bands are sometimes used for age-standardization calculations. Mortality rates are also calculated for specific causes of death, such as cholera, cancer, or suicide; and to monitor the control of infectious diseases, improvements in health care, or the social consequences of high unemployment.

Some mortality rates are already age-standardized. The infant mortality rate is the number of deaths within the first year of life divided by the number of live births in the same year times 1000. The neonatal mortality rate is the number of deaths within the first four weeks of life divided by the number of live births in the same year times 1000. The perinatal mortality rate is the number of still-births plus the number of deaths within the first week of life, divided by total births (still-births and live births) in the same year, again times 1000. The maternal mortality rate is the number of maternal deaths divided by total births times 1000. See also life-table ; morbidity statistics.