Measures of Dispersion
1. What is dispersion?
Degree to which numerical data tends to spread about an average value (or mean) is called variation or Dispersion of the data.
■ Some other important definations :-
- Dispersion is the measure of the variation of the items. - A. L. Bowley
- Dispersion is a measure of the extent to which the individual item vary. - L. R. Connor
■ There are various measures of dispersion but the most important are:
- Range
- Quartile Deviation
- Mean Deviation
- Standard deviation
■ There are two type of measures of dispersion :
1. Absolute measure of Dispersion :-
Measure of Dispersion which can be converted into same statical unit in which the original data are given. But the dispersion obtained from these measure cannot be used to compare the variability of two distributions expressed in different units
2. Relative measure of Dispersion :-
These measures are pure numbers independent of the units of measurement and can be used to compare the variability of two distribution expressed in different units.
⊙ Properties of a good measure of Dispersion:
- It should be simple to understand.
- It should be easy to calculate.
- It should be rigidly defined.
- It should be based on all observation.
- It should have sampling stability.
- It should not be unduly affected by extreme observation.
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