Measures of spread, or measures of variability, tell us how spread out a distribution is. For example, consider the below two histograms:
By viewing the histograms, we can clearly see that the distribution of data in Histogram A is more spread out than the distribution of data in Histogram B. Measures of spread can help us to quantify these types of differences in variability. The measures of spread we will consider in this section are the variance, standard deviation, interquartile range, and range. We will also consider the concept of quartiles.