Which of the following is NOT a common measure of dispersion?

The average, also known as the mean, is a measure of central tendency, not a measure of dispersion. Measures of dispersion are used to describe the spread or variability of a dataset.

Range, standard deviation, and quartiles all pertain to how data is distributed around the central tendency. The range provides a simple measure of the spread by calculating the difference between the highest and lowest values. Standard deviation offers a more sophisticated measurement, quantifying how much individual data points typically deviate from the mean. Quartiles divide the dataset into four equal parts, providing insights into the spread and relative standing of values within the data set.

In contrast, the average summarizes a set of values into a single representative number, giving no insight into the variability or spread of those values. Thus, it is accurate to identify the average as not belonging to the group of measures of dispersion.