It is relevant for measuring the average longevity of the population as a whole and is collected using well-established standards. Life expectancy can be measured at birth and at various ages. All life expectancies measure how long on average people could expect to live based on the age-specific death rates currently prevailing. Life expectancy at birth is, however, only an estimate of the expected life span of a given cohort, as the actual age-specific death rates of any particular birth cohort cannot be known in advance. Measures of life expectancy at birth refer to people born today and are computed by the OECD as the unweighted average of life expectancy for men and women. Life expectancy indicators meet a number of criteria characterising “ideal" indicators (Table 5.1), with the exception of the availability of disaggregated information across various population groups.