Dispersion

Mean deviation about mean For ungrouped data: , where is the mean given by

Mean deviation about mean For grouped data: , where is the mean given by and

Example:

Calculate mean deviation about mean for the following data:

Class

0 – 10

10 – 20

20 – 30

30 – 40

Frequency

21

19

49

11

Solution:

Here, assumed mean (a) = 25 and class size (h) = 10

Class

Frequency (fi)

Mid-point (xi)

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