Range is the simplest measure of dispersion — the difference between the largest and smallest values — and the coefficient of range is its relative (unit-free) version used to compare spread across data sets. Range shows absolute spread; the coefficient makes that spread comparable.

The formulas

where $L$ = highest value and $S$ = lowest value. For a frequency distribution, use the upper limit of the highest class as $L$ and the lower limit of the lowest class as $S$.

Worked illustration

Marks: 20, 35, 48, 60. Then $L = 60$, $S = 20$: Range $= 60 - 20 = 40$, and Coefficient of Range $= \dfrac{60 - 20}{60 + 20} = \dfrac{40}{80} = 0.5$. …