The mean deviation (also called the mean absolute deviation) is the mean of the absolute deviations of a set of data about the data's mean. For a sample size, the mean deviation is defined by. (1). where is the mean of the distribution. The mean deviation of a list of numbers is implemented in the Wolfram Language as. [ data ]. The mean deviation for a discrete distribution defined for, 2, ..., is given by. (2). Mean deviation is an important descriptive statistic that is not frequently encountered in mathematical statistics.