Worker skill is defined by educational attainment and therefore not the actual skill level of workers. Whilst this is not hugely problematic at the country level since the definition of skill levels does not vary within country, it can be cumbersome when calculating inequality at the global level. It also presupposes that educational attainment is directly linked to skill levels. Three other sources are identified. The first is the Gini coefficient from the Word Development Indicators (WDI) database—WDI Gini.