Dispersion is the variability around the central tendency (i.e. if mean addresses returns, then dispersion addresses risk).
Essentially, it shows how far the units are from the central tendency.
Absolute Dispersion is the amount of variability that is present, without comparison to any reference point or benchmark. They include (i) Range, (ii) Mean Absolute Deviation (“MAD”), (iii) Variance, and (iv) Standard Deviation.
Population Variance is the arithmetic average of the squared deviations around the mean
Population Standard Deviation is the square root of the “Population Variance”
Sample Variance is the sample measure of the degree of dispersion of a distribution
Variance and standard deviation takes into account returns above or below the mean. We may sometimes want to concentrate only on the downside risk