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.
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 {\displaystyle D_{1}} to D 9 {\displaystyle D_{9}} ( D 1 {\displaystyle D_{1}} = 10th percentile, D 2 {\displaystyle D_{2}} = 20th percentile and so on). It is calculated as follows:
D M = ∑ i = 1 9 D i 9 {\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.
See also Summary statistics Socio-economic decile (for New Zealand schools)
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