I am wondering the coefficient of variation for a sample is $\displaystyle \frac{s}{\bar{X}}$ or $\displaystyle |\frac{s}{\bar{X}}|$ because value of $\displaystyle \bar{X}$ can negative.
Anyone can help me? Thanks a lot.
Yes, $\displaystyle \overline x$ can be negative, but very rare. When it's negative, it will still not make any difference. Coefficient of Variance, is used for comparisons of data of different units. It tells us the relation between the two in percentage. A relative dispersion of -1% or 1% is the same. It's the same as saying that it's within $\displaystyle \pm $1%.