standard deviation for ratio of means
It is more generally a measure of spread. The mean is a measure of location. The ratio of the standard deviation to the mean is called the coefficient of variation. This can be helpful in distinguishing two data sets that are given in different units.For example if we are comparing economic data from two different countries, the data might be quoted in different currencies. similar ratio is the index of dispersion, which is the square of the standard deviation divided by the mean. In biology, for example, we might look at the locations of trees within a wood. An index of dispersion equal to 1 would indicate a dispersal consistent with a Poisson process, i.e. uniformly at random.