Income inequality measures how different the incomes might be between people in one society, whether that society is a county, province, state, country, or region of the world. Social scientists try to systematically estimate gaps between the poor, the rich, and everyone in between. Income inequality consists of the differences in the amount of money people receive in a year (e.g., differences between wages for blue- and pink-collar workers, salaries for white-collar workers and professionals, interest that accrues from investments, and anything else that comes into a person's wallet, purse, or bank account). A distinction is usually made between income and wealth, which is accumulated income from previous periods of income, from one to 100 years ago. Too much income inequality can be very harmful to society. Scholars differ on how much inequality is too much, but from 1890 to 1928, and from 1995 to the present, income inequality has...