Literally, dispersion means deviation, difference or spread of certain values from their central value. In relation to statistical seris, it means, deviations of various items of the series from its ventral value. Moreover, the word “measure refers to a method of measuring certain values. Thus, the phrase measure of dispersion referst to various possible methods of measuring the dispersions of different values from average value or any other extreme value.
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According to Simpson and Kafka, “The measurement of the scatter ness of the mass of figures in a series about an average is called a measure of variation or dispersion.”
According to W. I. King, “the term dispersion is used to indicate the facts that within a given group, the items differ from one another in size or in other words, there is lack of uniformity in their sizes.”
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According to Spiegel, “The degree to which numerical data tend to spread about an average value is called the variation or dispersion of the data.”
According to A. L. Bowley, “Dispersion is a measure of variation of the items.”
What are the Objects of Dispersion
To use other Statistical Methods
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After getting value of dispersion we can proceed to other technique such as to locate Co-relation or lines of Regression (Regression Analysis).
To Compare Variability
We are in the general habit of comparison, may it be income, weight, height or temperature. To achieve the required degree of result one tries to compare the variability in the data.
to test Reliability of Average
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If the total of differences between the central value and the given value is smaller, the uniformity is less i.e. it means that this sum should be minimum for the reliability of the average.
To establish trends in time Series
IN time series we remove, cyclical, seasonal or random fluctuations, which we form after studying central values.
to Control the Undesired Variability
According to Spurr and Bonini, “In matters of health, variations in body temperature, pluse beat and blood pressure are basic guides to diagnosis. Prescribed treatment is designed to control their variation. In industrial production, efficient operation requires control of quality variation, the causes of which are sought through inspection and quality control programmes.”