Mortality Rate

Mortality rate is a measure of the number of deaths (in general, or due to a specific cause) in a population, scaled to the size of that population, per unit of time. Mortality rate is typically expressed in units of deaths per 1000 individuals per year; thus, a mortality rate of 9.5 (out of 1000) in a population of 1,000 would mean 9.5 deaths per year in that entire population, or 0.95% out of the total. It is distinct from morbidity rate, which refers to the number of individuals in poor health during a given time period (the prevalence rate) or the number of newly appearing cases of the disease per unit of time (incidence rate). The term "mortality" is also sometimes inappropriately used to refer to the number of deaths among a set of diagnosed hospital cases for a disease or injury, rather than for the general population of a country or ethnic group. This disease mortality statistic is more precisely referred to as "case fatality rate" (CFR).

One distinguishes:

1. The crude death rate, the total number of deaths per year per 1000 people. As of July 2009 the crude death rate for the whole world is about 8.37 per 1000 per year according to the current CIA World Factbook.
2. The perinatal mortality rate, the sum of neonatal deaths and fetal deaths (stillbirths) per 1000 births.
3. The maternal mortality ratio, the number of maternal deaths per 100,000 live births in same time period.
4. The maternal mortality rate, the number of maternal deaths per 1,000 women of reproductive age in the population (generally defined as 15–44 years of age) .
5. The infant mortality rate, the number of deaths of children less than 1 year old per 1000 live births.
6. The child mortality rate, the number of deaths of children less than 5 years old per 1000 live births.
7. The standardised mortality ratio (SMR)- This represents a proportional comparison to the numbers of deaths that would have been expected if the population had been of a standard composition in terms of age, gender, etc.
8. The age-specific mortality rate (ASMR) - This refers to the total number of deaths per year per 1000 people of a given age (e.g. age 62 last birthday).

In regard to the success or failure of medical treatment or procedures, one would also distinguish:

1. The early mortality rate, the total number of deaths in the early stages of an ongoing treatment, or in the period immediately following an acute treatment.
2. The late mortality rate, the total number of deaths in the late stages of an ongoing treatment, or a significant length of time after an acute treatment.

Note that the crude death rate as defined above and applied to a whole population can give a misleading impression. The crude death rate depends on the age (and gender) specific mortality rates and the age (and gender) distribution of the population. The number of deaths per 1000 people can be higher for developed nations than in less-developed countries, despite life expectancy being higher in developed countries due to standards of health being better. This happens because developed countries typically have a completely different population age distribution, with a much higher proportion of older people, due to both lower recent birth rates and lower mortality rates. A more complete picture of mortality is given by a life table which shows the mortality rate separately for each age. A life table is necessary to give a good estimate of life expectancy.