Q.From the following the one which is a relative measure of dispersion is :

Relative measures are ratios/coefficients; here that is the coefficient of mean deviation.

Measures of dispersion are of two kinds:

• Absolute — expressed in the original units (Range, Quartile deviation, Mean deviation, Standard deviation).
• Relative — a unit-free ratio obtained by dividing an absolute measure by an average (Coefficient of range, Coefficient of quartile deviation, Coefficient of mean deviation, Coefficient of variation). …

$\bar{x}=18$, $\text{M.D.}=\frac{8+6+2+12}{4}=7$.

Mean:

$\bar{x}=\frac{10+12+20+30}{4}=\frac{72}{4}=18.$

Absolute deviations from the mean:

$|10-18|=8,\;|12-18|=6,\;|20-18|=2,\;|30-18|=12.$

…

Coefficient of M.D. $=\dfrac{\text{Mean deviation}}{\text{average used}}$.

A relative measure of dispersion is formed by dividing the absolute measure by the corresponding average. For mean deviation taken about the mean,

$\text{Coefficient of M.D.}=\frac{\text{Mean deviation}}{\text{Mean}}.$

…