Income distribution refers to how a country's total national income is divided among individuals, groups, or factors of production. Unequal income distribution can harm economic performance by reducing productivity and increasing health and education costs for the poor. Theories of income distribution examine factors like functional income distribution between labor and capital as well as individual income size distribution. Common measures of inequality include the Lorenz curve, Gini coefficient, and economic mobility between income quintiles. While some inequality may promote growth by incentivizing education and entrepreneurship, excessive inequality can concentrate power and resources, reduce opportunity, and increase economic and political instability.