This document provides information about calculating the mean absolute deviation and coefficient of dispersion for grouped and ungrouped data: - The mean absolute deviation is the average of the absolute differences between observations and the central value (mean, median or mode). - Formulas are given for calculating the mean absolute deviation about the median for ungrouped and grouped data. - An example shows how to calculate the mean deviation from the median and coefficient of dispersion for a set of ungrouped data and for grouped data from a frequency distribution. - Practice problems are included for the reader to calculate these measures of dispersion.