Decile

In descriptive statistics, a decile is any of the nine values that divide the sorted data into ten equal parts, so that each part represents 1/10 of the sample or population.¹ A decile is one possible form of a quantile; others include the quartile and percentile.² A decile rank arranges the data in order from lowest to highest and is done on a scale of one to ten where each successive number corresponds to an increase of 10 percentage points.

A moderately robust measure of central tendency, known as the decile mean, can be computed by making use of a sample's deciles ${\displaystyle D_{1}}$ to ${\displaystyle D_{9}}$ (${\displaystyle D_{1}}$ = 10th percentile, ${\displaystyle D_{2}}$ = 20th percentile and so on). It is calculated as follows:³

${\displaystyle DM={\frac {\sum _{i=1}^{9}D_{i}}{9}}}$

Apart from serving as an alternative for the mean and the truncated mean, it also forms the basis for robust measures of skewness and kurtosis, and even a normality test.⁴