Measures of DispersionA measure of dispersion is the amount of scattering of individual values from the measure of central tendency.
 
The degree to which numerical data tends to spread about an average value is called the dispersion of the data.
 
There are two measures of dispersion
Absolute measures of dispersionRelative measures of dispersion
The absolute measures of dispersion are:
RangeQuartile deviationMean DeviationStandard Deviation
The relative measures of dispersion are:
Coefficient of rangeCoefficient of quartile deviationCoefficient of mean variationCoefficient of variation
The relative measures of dispersion are used for the purpose of comparing two or more sets of data.
 
Why are measures of dispersion helpful?
 
Consider three students with the following test scores:
 
Caroline:
50%, 60%, 70%, 80%, 90%
Average = 70%
George:
70%, 70%, 70%, 70%, 70%
Average = 70%
Henry:
90%, 90%, 90%, 50%, 30%
Average = 70%
 
Although these three students have the same average of 70%, we can see that their performances are vastly different.
Caroline's grades have improved. Difference of 40% between lowest and highest scores.George's grades have remained the same. He is very consistent! Difference between any two scores is 0%.And, Henry's grades have dropped. Difference of 60% between lowest and highest scores.Various measures of dispersion will help differentiate these three student's performances.