Normally distributed data can be described by the mean and standard deviation (or variance). However, not normally distributed data requires further descriptive statistics. To describe the central tendency, the **mode** (most common category) and **median** (equal number of measurements above and below) are used in addition to the **mean**. The dispersion of data can be described with the **range** (interval from lowest to highest value), **interquartile range** (the difference between the upper and lower quartiles), or **minimum** and **maximum** values.

Distributions that are not Normal, are not necessarily symmetrical around the mean and can be skewed. The plot below shows the mode, median and mean in a **right skewed** distribution (a right skewed distribution has a ‘tail’ to the right, a left skewed distribution a ‘tail’ to the left):

In a Normal distribution, the mean, mode and median are the same.