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. A decile is one possible form of a quantile; others include the quartile and percentile. 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.

Special Usage: The decile mean

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

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

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.

See also

• Summary statistics
• Socio-economic decile (for New Zealand schools)