It also has linkages with indicators of human health and the environment as well as economic indicators. Examples of closely linked indicators would include infant mortality, and water and air quality. Methodological Description and Underlying Definitions Calculation of life expectancy at birth is based on age-specific death rates, which may be calculated separately for males and females, or for both sexes combined. Where data on deaths by age are of good quality, or adjustments for age mis-statement and incompleteness can be made, the life expectancy at birth can be calculated directly from registered deaths and population counts, which are usually based on census enumerations, evaluated and, if necessary, adjusted. Assessment of the Availability of Data from International and National Sources Data is collected by the United Nations on a regular basis and available for most countries from vital registration systems or surveys.
Most countries tabulate data from death registration systems at the sub- national level.
The 1994 Revision. United Nations Sales No. E.95.XIII.16, New York, 1995. E.83.XIII.2, New York, 1983. The United Nations Software Package for Mortality Measurement.