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Unit 7: Measures of Dispersion
6. It should not be unduly affected by extreme observations. Notes
7. It should not be much affected by the fluctuations of sampling.
Self Assessment
Fill in the blanks:
11. A good measure of dispersion should be .........................defined.
12. A good measure of dispersion should be ...................................... all the observations.
13. A good measure of dispersion should not be unduly affected by .................................
14. A good measure of dispersion should not be much affected by the .......................... of
sampling.
7.4 Measures of Dispersion
Various measures of dispersion can be classified into two broad categories:
1. The measures which express the spread of observations in terms of distance between the
values of selected observations. These are also termed as distance measures, e.g., range,
interquartile range, interpercentile range, etc.
2. The measures which express the spread of observations in terms of the average of deviations
of observations from some central value. These are also termed as the averages of second
order, e.g., mean deviation, standard deviation, etc.
The following are some important measures of dispersion
(a) Range
(b) Inter-Quartile Range
(c) Mean Deviation
(d) Standard Deviation
Self Assessment
State whether the following statements are true or false:
15. The measures which express the spread of observations in terms of distance between the
values of selected observations are termed as Kilometres measures.
16. The measures which express the spread of observations in terms of the average of deviations
of observations from some central value. These are also termed as the averages of second
order, e.g., mean deviation, standard deviation, etc.
17. An absolute measure of dispersion is expressed in terms of the units of measurement of
the variable.
18. A relative measure of dispersion, popularly known as coefficient of dispersion, is expressed
as a pure number, independent of the units of measurement of the variable.
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