Without knowing something about how data is dispersed, measures of central tendency may be misleading.
Measures of dispersion provide a more complete picture.
The range is perhaps the simplest measure of dispersion. It is calculated by simply taking the difference between the maximum and minimum values in the data set. However, the range only provides information about the maximum and minimum values and does not say anything about the values in between. However, performing this calcuation will result in an average deviation of zero since the values above the mean will cancel the values below the mean. If this method is used, the absolute value of the difference is taken so that only positive values are obtained, and the result sometimes is called the mean absolute deviation .