They are very well documented for all countries and years and available by age, gender14, and in some countries, by educational attainment (Sen 1998, Mackenbach et al. Also, there are large and persistent inequalities in longevity within countries that tend to be correlated with the socio-economic background of individuals. Furthermore, the socio-economic determinants of inequality in longevity, such as the education gradient of mortality, are very different across OECD countries.