Beginners:Statistical concept - Quintile and decile
This page is part of Statistics 4 beginners, a section in Statistics Explained where statistical indicators and concepts are explained in a simple way to make the world of statistics a bit easier both for pupils and students as well as for all those with an interest in statistics.
When you sort a set of data and divide it into equal parts so that each part contains the same number of values, these cut-off points are called quantiles.
For instance, when a set of data is divided into five equal parts, each of them is called a quintile, which refers both to the cut-off points as well as the group of values contained. When a set of data is divided into ten equal parts, each of them is called a decile.
Example
In the field of income statistics, quintiles are used to find out how income is distributed among the population. To illustrate this, the population is first divided into five equal parts depending on their level of income: the first quintile contains the bottom fifth of the population on the income scale (i.e. the 20 % of the population with the lowest income), the second quintile represents the second fifth (from 20 % to 40 %) etc.; and the fifth quintile represents the 20 % of the population with the highest income.