2.1 The figures for 2004-2006 are a three year average. They are produced by aggregating deaths and population data for the three year period. Three years of data is needed to provide large enough numbers to ensure that the figures published in this report are sufficiently robust.
2.2 Period life expectancy at birth for a given time period and area is an estimate of the average number of years a new born baby would survive if he/she experienced the particular area’s age specific mortality rates for that time period throughout his/her life. The figure reflects mortality among those living in the area in each period, rather than mortality among those born in each area. It is not the number of years a baby born in the area during the three year period is expected to live, both because death rates are likely to change in the future and because many of the new borns may live elsewhere for at least some part of their lives.
2.3 Life expectancy at birth is also not a guide to the remaining expectancy of life at any given age. It reflects the fact that survival from a particular age depends only on mortality rates beyond that age, whereas survival from birth is based on mortality rates at every age. Table 4 and Table 5 show life expectancy at an "exact age". Life expectancy at birth provides a useful summary measure of mortality rates actually experienced over a given period and, for past years, provides an objective means of comparison of the trends in mortality over time, between areas of a country and with other countries. More information on the methodology used is given in Section 4.2.