Define Mean Deviation (M.D).Mention its merits and demerits.
Mean Deviation: For a given set of observation, MD is defined as the arithmetic mean of the absolute deviation of the observations from an appropriate measure of central tendency.
The formula for computing MD is
MD= ∑│D│/ N
MD is an absolute measure of dispersion. The relative measure corresponding to MD, called the coefficient of MD, is obtained by dividing mean deviation by the particular average used in computing mean deviation. Thus, if MD has been computed from median, the coefficient of mean deviation shall be obtained by dividing MD by median.
• Coefficient of Mean Deviation = MD/ (Mean or Median)
Merits of Mean Deviation:
1. It is simple to understand and easy to compute.
2. It is based on each and every item of the data.
3. MD is less affected by the values of extreme items than the Standard deviation.
Demerits of Mean Deviation:
1. The greatest drawback of this method is that algebraic signs are ignored while taking the deviations of the items.
2. It is not capable of further algebraic treatments.
3. It is much less popular as compared to standard deviation.