Gini coefficient

The Gini coefficient (also known as the Gini index or Gini ratio) is a measure of differences in income. It was developed by the Italian statistician Corrado Gini in 1912.
Definition.
The Gini coefficient is usually a number between 0 and 1 (or 0 to 100). 0 means a country where the income is equally distributed. On the other hand, 1 means that one person owns everything but the rest owns nothing. In reality, all scores are between 0.25 and 0.6 (between 25 and 60 on the 0 to 100 scale).
Statistics.
The table below is about the "world" Gini coefficient (not by single countries).
The table below shows the income Gini coefficient of the United States from 1947 to 2009.