Uncontrolled variation is the enemy of quality . - Edward Deming
In our previous courses, we have studied classification, tabulation and the measures of central tendency of the collected data. As we know now, any measures of central tendency or averages of data represent the summary or central value of data. It may happen that some observations of the data are very near to the central value while some are very far. So, it is useful to know how the observations are scattered from the central values of the population. Though measures of central tendency are very useful in statistical analysis, they are not sufficient. In order to know how the observations are scattered, we need the help of measures of dispersion.
Meaning and characteristics of dispersion, absolute and relative measures of dispersion, Range, Quartile Deviation, Average Deviation, Standard deviation, Combined standard deviation