mortality

Meaning: Mortality is the occurrence of death in a population. With fertility and migration, it is one of three demographic processes that change population size. It is reported as rates: crude death rate, age-specific rates, and infant mortality rate (deaths before age 1 per 1,000 live births). Rates differ by social class, race and ethnicity, gender, and country.

Equation: Crude death rate = (D ÷ P) × 1000, where D is deaths in a year (a count) and P is the midyear population (persons). The result is deaths per 1,000 people per year, a rate rather than an SI quantity.

On the MCAT: Expect a table of death rates or a demographic transition graph. In stage 2, mortality falls from better sanitation, nutrition and medicine while birth rates stay high, so population grows quickly. Population change = (births − deaths) + (immigration − emigration). Lower-income groups usually show higher mortality.

Common confusion: Mortality is death; morbidity is illness. A common illness can have high morbidity and low mortality. Also, the crude death rate depends on age structure, so an older wealthy country can have a higher crude rate than a younger poorer one; age-adjusted rates remove that effect.