A quintile measure is a statistical term used to divide a population into five equal groups according to a particular variable. In economics, quintile measures are useful for socio-economic purposes, such as determining the lifestyle of the top 20% of a population or the lowest 20%. It can also determine what level of income a family needs to have to leave the lowest 20% .
The United States Census Bureau records and tabulates the percent share of income held by each quintile of the population each year. In the following graph, created by using the data in US Census Bureau table F2: All Races, it can be observed that the top 5th of the population has acquired an increasingly larger share of total income over the past 3 decades.