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A fifth portion or band of a set of data. A quintile is a proportion of a set of data that has been ranked and divided into five equal groups (or bands), where each group contains an equal number of data items.

For example, consider the (ordered) data set of 20 letters:

"A A A B B C D E F G G H I J K L L M N N N".

The first quintile would contain "A A A B", the second quintile "B C D E", the third "F G G H", the fourth "I J K L L" and the fifth "M N N N". Ideally each quintile would contain the same number of elements, but this isn't always possible in practise.

See also decile, percentile.