Summary

• Measures of dispersion are range, mean deviation, variance and standard deviation.
• Range = [largest value - smallest value].
• Mean deviation for an ungrouped data: MD; M.D(M)
• Mean deviation for grouped data: MD; M.D(M)
• Variance and S.D for ungrouped data:
• Variance and S.D for ungrouped data using assumed mean:
• Variance and S.D of a continuous frequency distribution:
A is assumed mean h is the common factor for all deviations.

• Coefficient of variation (C.V) = ,
• For two or more series with equal means, the series with lesser S.D is more consistent and less scattered.
• For comparision of two or more sets of data, the one which has least C.V is more consistent and less scattered