What is the name of the statistical measure of income inequality that ranges from 0 to 1?

The statistical measure of income inequality that ranges from 0 to 1 is the Gini coefficient.

Developed by Italian statistician Corrado Gini and published in 1912, the coefficient summarizes how unevenly income or wealth is distributed. A value of 0 represents perfect equality, where everyone has the same income. A value of 1 represents theoretical maximum inequality, where one person receives all the income and everyone else receives none. In real-world income data, values normally fall between those extremes.

The measure is derived from the Lorenz curve, which compares the cumulative share of income received by a cumulative share of the population. The Gini coefficient is related to the area between that curve and the line representing perfect equality. Depending on the dataset, analysts may calculate it before or after taxes and transfers, so two Gini figures for the same country can measure different distributions.

The Gini coefficient is not a ranking of average prosperity. A country can have a high average income and substantial inequality, while another can be poorer but more equal. The Lorenz curve is the underlying graphic; the Gini coefficient is the numerical summary.