4 Data exploration
4.5 Measures of dispersion

Measures of central tendency aim to identify the most representative value of a data set, that is, the centre of a distribution. To better describe the data, it is also good to have a measure of the spread of the data around the centre of the distribution. This measure is called a measure of dispersion. The most commonly used measures of dispersion are

• The range, which is the difference between the highest value and the smallest value;
• The interquartile range, which is the range of the 50% of data that is central to the distribution;
• The variance, which is the mean squared distance between each point and the centre of the distribution;
• The standard deviation, which is the square root of variance.

The following sections explain how to calculate these measures using examples. Measures of dispersion are applicable to numeric variables only.