Income inequality is the difference in the average income of the lower/middle class and the upper class.
Naturally the high income of very rich people in the country, which constitute a very small percentage of the population, will dwarf the average income of those who are not very rich. The worrisome thing is when the gap between them widens at an accelerating rate and the lower classes are not able to break through to the upper classes.
Income inequality is a field of study that focuses on the average income and standard of living of the average lower- and middle-class families in a country and compares it to that of the upper-class citizens. Some countries do not have a large disparity between the two, while some have a very wide gap.
Naturally some people will have more skills and education, better ideas and better work ethic than some other people, but when one person is paid far higher amounts for the same amount of work that may or may not have much utility value in society, this is income inequality.
Having a higher income and more money tends to enable a person to make an even greater amount of money in the future, which further increases income inequality. Social mobility is a closely related concept, which has to do with the ability in a society of a member of one socio-economic class to move up into the other, higher-income tiers.
This is a large part of the mythos of the American Dream: that through hard work, anyone could become as successful as anyone else. A large wealth gap, which is another word for income inequality, tends to stifle social mobility, according to some studies.
The United States has among the highest levels of income inequality in the worth. It is measured with such statistical tools as the Gini Coefficient.
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