Coefficient of variation

A dimensionless measure of the spread of the distribution of a random variable. This coefficient may be defined in several ways. In practice, its most frequent definition is by the formula

$$V=\frac\sigma\mu,$$

where $\sigma^2$ is the variance and $\mu$ is the mathematical expectation ($\mu$ must be positive). This expression is often used in its percentage form, viz., $V=100\sigma/\mu$ %. This definition was proposed in 1895 by K. Pearson.