Life Expectancy

Column 1 refers to the age intervals of each group. The entries refer to the range of years between two birthdays. For example, the age group 5–9 refers to the 5-year interval between the 5th and the 10th birthdays.

Column 2 reports for each age group the agespecific death rates, designated as nMx. These are the only empirical data needed to build a life table.

Column 3 reports for each age group the probabilities of dying, designated as nqx. This is the most basic column of the life table; the probabilities are derived from the death rates in column 2. The column 3 data are the probabilities that persons who are alive at the beginning of an age interval will die during that age interval, before they reach the start of the next age interval.

Column 4 presents data on the number of people alive at the beginning of the age interval, designated as lx. This column of data is calculated by subtracting the ndx value (column 5) from the lx value in the age interval immediately preceding the one being calculated.

Column 5 shows the number of people who die during a particular age interval, designated as ndx, and is determined by multiplying lx by nqx.

Column 6 reports for each age interval the total number of years lived by all persons who enter that [Page 649]age interval while in the age interval. The nLx values are roughly given by the formula, nLx = (1x − 1/2 ndx (n).

Column 7 reports the total number of years lived by the population in that age interval and in all subsequent age intervals, and is designated as Tx. To determine the values of Tx for each age interval, one sums the nLx from the oldest age backward.

...