Educational attainment refers to the highest level of formal education completed by the members of a population. Because national systems of education differ greatly from one another, the measurement of educational attainment is typically restricted to education completed in the country where the education was received, although researchers have developed various metrics to translate levels of completed schooling across countries. Educational attainment is sometimes recorded as the number of years of schooling that individuals have completed, but is more often measured as the highest grade or highest level completed. The distinction between years of schooling and highest level completed is particularly important in highly schooled and highly economically developed societies in which primary and secondary schooling are virtually universal. Moreover, in highly economically developed societies distinctions at the upper levels of the educational distribution are of more social consequence than distinctions expressed simply in years of schooling.