Question

Describe the three basic methods for contructing a life table (2 main methods, one of which has 2 submethods). For each one explain how data are collected and entered into a life table. Identify a positive and negative aspect for each.

Answer 1

Methods of constructing life table:

Life tables are used to compute life expectancy at birth and at different ages, but they are also used to compute many other indicators: death probabilities, probabilities of survival between two ages, number of years of life lived and the number of survivors at different ages. The construction of a life table makes it possible to summarize mortality within a population at a given time (period life table) or within a cohort (cohort life table). Period life tables are constructed on the basis of a single cross-sectional time data for a generation. But in contrast, cohort life table is a longitudinal life table method which takes a real cohort of persons that start life at a specific age interval and follow it throughout life until they die.

Further cohort life table could be constructed in two ways. In one way it may be constructed on the basis of single years of ages. And other is an abridged life table, can also be constructed wherein ages are grouped in 5 or 10 years of interval, taking the intial year as 0-1.

Major components of a life table:

m_x

Definition - This is known as the central rate of mortality. That is the average number of deaths each year at age x last birthday in the relevant three-year period, divided by the average population at that age over the same period.

Example - mx for age 70 years in 2015 to 2017 would be the average number of deaths at age 70 years across 2015, 2016 and 2017, divided by the average number of people aged 70 years across 2015, 2016 and 2017.

q_x

Definition - This is the mortality rate between age x and (x +1). That is, the probability that a person aged x exactly will die before reaching age (x +1).

Example - qx for age 70 years in 2015 to 2017 would be the probability that a person aged 70 years exactly in 2015, 2016 or 2017 will die before reaching age 71 years.

l_x

Definition - This is the number of males or females surviving to exact age x of 100,000 live births who are assumed to be subject throughout their lives to the mortality rates experienced in the specified three-year period.

Example - lx for age 70 years in 2015 to 2017 would be the number of males or females out of 100,000 live births in 2015 to 2017 expected to survive to age 70 years calculated using the age specific mortality rates applicable for 2015 to 2017.

d_x

Definition - This is the number of males or females dying between exact age x and (x +1) described similarly to lx, that is, d_x = l_x – l_x+1.

Example - dx for age 70 years in 2015 to 2017 would be the number of males or females out of 100,000 live births in 2015 to 2017 expected to die between age 70 and age 71 years.

e_x

Definition - This is the average period life expectancy at exact age x, which is the average number of further years that those aged x exactly will live based on the mortality rates experienced in the specified three-year period.

Example - ex for age 70 years in 2015 to 2017 would be the average number of further years that a person aged 70 years exactly in 2015, 2016 or 2017 could expect to live if they experienced the age-specific mortality rates of the given area for 2015 to 2017 for the rest of their life.