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MEAN DEVIATION (M.D.)

If x1,x2,………………,xn be the n observation then M.D is defined as

Where A may be mean (.X), or median or mode.

For simple frequency distri0ution, M.D. is defined as

 

where A may be mean (.X) or median or mode.

For grouped frequency distribution, x will be taken as class-mark.

Sometimes M.D. about mean (.X) is called simply M.D.

Note. 1. M.D. taken about median is the least, compared to M.D. taken about mean (.X) or mode.

2. It is not a very accurate measure of dispersion particularly when it is calculated from mode.

3. S.D.> M.D.