Mortality is the condition of being mortal, or susceptible to death;
Mortality rate is a measure of the number of deaths (in general, or due to a specific cause) in some population, scaled to the size of that population, per unit time. Mortality rate is typically expressed in units of deaths per 1000 individuals per year; thus, a mortility rate of 9.5 in a population of 100,000 would mean 950 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 who currently have that disease (the incidence rate), scaled to the size of the population.
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 rate, the number of maternal deaths per 100,000 women of reproductive age in same time period.
4. The infant mortality rate, the number of deaths of children less than 1 year old per 1000 live births.
5. The child mortality rate, the number of deaths of children less than 5 years old per 1000 live births.
6. The standardised mortality rate (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.
7. 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.
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.
Mortality displacement denotes a (forward) temporal shift in the rate of mortality in a given population, usually attributable to environmental phenomena such as heat waves or cold spells.
During heat waves, for instance, there is usually an excess mortality rate in the population, affecting especially older adults and those who are sick. For some heat waves, however, there has also been observed a decrease in overall mortality during the subsequent weeks after a heat wave. Such short-term forward shift in mortality rate is also referred to as harvesting effect. The subsequent, compensatory reduction in mortality suggests that the heat wave had affected especially those whose health is already so compromised that they "would have died in the short term anyway"
Mortality drag is a term used, in reference to life time annuities, to describe a negative impact that is experienced when an annuity purchase is delayed on a fund from which regular withdrawals are being taken by an individual. It is the increasing risk of falling annuity rates, and grows exponentially as an individual continues to defer an annuity purchase. In practical terms, it represents the extra investment return a customer has to achieve to justify not annuitizing a pension fund.
How a lifetime annuity works
In simple terms, a lump sum is given to an insurance company that agrees to pay a regular payment over the expected lifetime of an individual. This payment may be based on interest rates or returns on investments, and will take into consideration costs (and profits). It may be helpful to think of it as a loan in reverse, from the perspective of the individual purchasing the annuity. Those who live longer than the mean lifespan of an annuity population are effectively subsidised by those who die earlier and the insurance company usually assumes the risk of making this work based on actuarial assumptions. This is known as a "cross subsidy". An individual may therefore suffer a "mortality loss" or "mortality gain" based on when they actually die. This is a risk they take on board in exchange for a guaranteed income for the rest of their (uncertain) lives.
Delaying an annuity
When an individual delays buying an annuity, say between the ages of 60 and 65, the following will occur:
1. Some of the population who purchased an annuity at the age of 60 will have died, meaning their subsidy has been lost to those purchasing at 65.
2. While the total expected remaining lifespan will have decreased, the mean age of death in an annuity population entering at age 65 will be greater than for a group purchasing at age 60.
In practical terms, those who invested instead of purchasing an annuity may gain more from the growth of the investment than they lose in the delayed annuity rate. However, where an individual decides to take withdrawals from a given lump sum before buying an annuity, the impact of mortality drag becomes very significant and increases exponentially with age.