Life Table
Life tables measure the proportion of individuals surviving through various age groups. They are widely used in biological, medical, actuarial and social research. In life tables, age-specific death rates for a given population are usually established by tracking the mortality of a population over a period of time. Life tables are often used in conjunction with data on fertility and migration to construct population projections.
The term life table was originally introduced in 1740 by Edmund Halley. Halley was looking for the probability of surviving up until a given age, which was of great interest to insurers of that era. He used a population of adult males’ life expectancies from German states at the time and found that the mortality rate was highest among infants and young children, and then decreased with age up to a maximum between the ages of 30 and 40.
Life tables are created by applying measures of mortality at specific ages to a hypothetical group of persons, often called a cohort, who are all the same age at a particular time. A life table starts with all individuals assumed to be alive at a certain age, defined as the “starting age” and progresses through age-group changes (one-year increments in most cases).
To construct a life table, the cohort is divided into age groups and then the mortality rate is calculated for each age group, that is, the rate of death in the next year divided by the population at risk. We use the Kaplan-Meier method, which involves setting up a continuous interval estimate of death as opposed to exact numbers. Mortality rates for each age group are used to calculate the expectation of life for that age group. This is done by simply adding the years of expected life remaining in each age group together until the age of 100.
The output of a life table shows the mortality rate for each age group, the probability of dying in that age group, and years of expected life remaining until age 100. From this, we can calculate the probability of survival up to any given age and the average life expectancy of a population.
The use of life tables are important for many reasons. They are a way of monitoring mortality in a population and tracking changes in mortality rates over time. Life tables can be used to study health trends – for instance, to measure the effect of preventive health care activities or diet changes on mortality rates. They can also be used to estimate life expectancy, which can inform government policy decisions, such as retirement age. Life tables can also be used to assess health inequalities across different age groups or between different population groups.
Life tables provide an effective, quantitative way of studying mortality and health in a population. They are relatively simple to construct but, when combined with other data sources, can be used to understand more clearly the mortality trends in a population. Over the years, life tables have been used to evaluate improvements in life expectancy for a population, often at critical decisions such as pension reform or health care reform. This makes them an invaluable tool in public health research and policymaking.
