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

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


 * $$\frac{3 + 9 + 7 + 3 + 6 + 10 + 4}{7} = 6$$


 * 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.