## Summary

The range, inter-quartile range and standard deviation are all measures that indicate the amount of variability within a dataset. The range is the simplest measure of variability to calculate but can be misleading if the dataset contains extreme values. The inter-quartile range reduces this problem by considering the variability within the middle 50% of the dataset. The standard deviation is the most robust measure of variability since it takes into account a measure of how every value in the dataset varies from the mean. However, care must be taken when calculating the standard deviation to consider whether the entire population or a sample is being examined and to use the appropriate formula.