# Handbook of Descriptive Statistics/Measures of Statistical Variability/Standard Deviation

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**Descriptive Statistics**

*Descriptive Statistics* is statistical measures that are used to describe numerical data; this numerical data can be in form of a table, number list, frequency distribution etc.

Common Statistical measures are **arithmetic mean (AM)** (or average or simply the **mean**), **median**, **mode** and **standard deviation**.

**Arithmetic Mean (or average or mean)**- Arithmetic Mean (AM) of a list of
*n*numbers is defined as the sum of*n*numbers divided by*n*. This is a kind of center of the number list or simply the average of the number list. The order of numbers in the list is not important. - For example, the
**AM**of the number list 3, 8, 7, 3, 5, 10, and 2 is

**Median**- Median is another type of central tendency of list of numbers. To calculate the median of list of
*n*numbers, first the numbers should be arrange in ascending order i.e. from smallest to greatest. If*n*is odd then the median is defined as the middle number, if*n*is even then the median is defined as the average of two middle numbers. The order of the numbers is important for this tendency.