# Concepts and definitions

Glossary of concepts (terms) and their definitions relating statistical concepts.

### Income deciles

For employees average monthly income per year is calculated summing up income of all months of the year and dividing to the number of months worked.

All employees are arranged by their income in an ascending order, and successively divided into ten equal groups according to the number of employees. Each group includes 10% of all employees. Deciles are the highest income values of these groups.

The first decile shows that income of 10% of employees is less or equal to the highest value of the first decile. The second decile is equal to the highest income value of the second group. Similar approach is used for other deciles. The tenth decile is equal to highest income value of the tenth decile. Due to the fact that the tenth decile is equal to the highest value of income of all employees, the tenth decile is confidential and is not published. In turn the 5th decile at the same time is the median - half of the employees receive smaller or equal income to the value of the 5th decile, and the other half - greater or equal income to the value of the 5th decile. Usually the median value of employment income is smaller than the arithmetic mean value. The difference between the median and the arithmetic mean value shows the income distribution asymmetry. If the distribution was completely symmetrical, the median and the arithmetic average would be the same.