An index of dispersion is also needed.
Variability is a description of the tails of our curve - that is of the spread of scores.
So range can be helpful, but is the most unstable measure of variability there is. Because it is determined by only 2 scores. There are other types of ranges used. To understand them, you must understand percentiles , quartiles , and deciles . Several of the centile points have special names, such as median for C50.