The measure of spread to use will depend on which average value you have chosen to report for your dataset. As a general guide:
- If you have reported the mode then you could report the range of the data.
- If you have reported the median then you could report the interquartile range of the data.
- If you have reported the mean then you could report the standard deviation of the data.
| Range | The range of a data set is the difference between the smallest and largest values in the data set. To calculate the range, subtract the smallest number from the largest number (Range = Maximum - Minimum). | |||
Example of range by Maths is Fun. The range can be calculated in Excel by taking the difference between the maximum value and the minimum value of the dataset. | ||||
| Interquartile range | The interquartile range (IQR) captures the middle 50% of ordered data. To calculate, order data from smallest to largest. Find the values that are at the first (Q1) and third (Q3) quartile (or 25% and 75% along). The interquartile range is the difference between the third and first quartile (IQR = Q3 - Q1). Note: the second quartile is the median (Q2). | |||
Example of interquartile range by Maths is Fun. The interquartile range can be calculated in Excel by taking the difference between the third (=QUARTILE.EXC(datarange,3)) and first (=QUARTILE.EXC(datarange,1)) quartiles. | ||||
| Standard deviation | The standard deviation captures on average, how much each data point varies from the mean of the data set. | |||
Example of standard deviation by Maths is Fun. How to calculate the population standard deviation using Excel. How to calculate the sample standard deviation using Excel. | ||||
- A short guide from the Statstutor with examples of how to perform the measures of spread calculations by hand and SPSS.
- Practical examples and illustrations of measures of spread by Laerd statistics.