Measures of Dispersion — Important Questions

Should be based on all observations, Should be clearly defined, Should be simple to compute

A good measure of dispersion should be clearly defined, based on all observations, simple to compute, and suitable for further calculations. It should not be unduly affected by extreme values.

10

Quartile deviation = (Q3 - Q1)/2 = (40 - 20)/2 = 20/2 = 10

Range, Quartile Deviation

Range and quartile deviation are positional measures because they depend on the positions of observations when arranged in order. Mean deviation and standard deviation are based on deviations from central tendency.

Absolute values of deviations from mean

Mean deviation uses absolute values |xi - x̄| to overcome the problem that sum of deviations from mean equals zero. This gives the average absolute deviation from the mean.