All these merits of standard deviation make SD as the most widely and commonly used
measure of dispersion.
Range is the quickest to compute and as such, has its application in statistical quality
control. However, range is based on only two observations and affected too much by the
presence of extreme observation(s).
Mean deviation is rigidly defined, based on all the observations and not much affected by
sampling fluctuations. However, mean deviation is difficult to comprehend and its
computation is also time consuming and laborious. Furthermore, unlike SD, mean deviation does not possess mathematical properties.
Quartile deviation is also rigidly defined, easy to compute and not much affected by sampling fluctuations. The presence of extreme observations has no impact on quartile deviation since quartile deviation is based on the central fifty-percent of the observations. However, quartile deviation is not based on all the observations and it has no desirable mathematical properties. Nevertheless, quartile deviation is the best measure of dispersion for open-end classifications.