If a distribution of salaries, income, turnover, etc. are put in order, deciles are the values that divide that distribution into ten equal parts.
As such, for a distribution of salaries :
- the first decile (generally written D1) is the salary below which 10% of salaries are situated ;
- the ninth decile (generally written D9) is the salary below which 90% of salaries are situated.
The first decile is, in the same respect, the salary above which 90% of salaries are situated; the ninth decile is the salary above which 10% of salaries are situated.