For example, less than half of boys of primary school age in South Sudan were attending school in 2015, only about one third of girls were in school. Similarly low levels of primary school enrolment are seen in countries such as the Democratic Republic of the Congo and Liberia. The Gini Coefficient is a measure of income distribution in a country and is the most commonly used measure of income inequality. The graph suggests that countries with young age structures are generally more unequal in terms of income.