Dispersion: - Dispersion refers to the scatteredness of the individual items of statistical series from their central value. So a descriptive measure of scatter of the values about the average is called measure of Dispersion. The followings are the important methods for measure of dispersion: The Range The average/mean Deviation Quartile Deviation The 10 – 90 Percentile Range The Standard Deviation The Variance The Range: - The Range of a set of numbers is the difference between the largest and smallest numbers in the set. The average/mean Deviation: - The average/mean Deviation, of a set of N numbers X 1 , X 2 ,……..X N is abbreviated MD and is defined by Quartile Deviation: - Quartile Deviation, of a set of data is denoted by Q and defined by,Q = (Q 3 – Q 1 )/2 The 10 – 90 Percentile Range : - The 10 – 90 Percentile Range, of a set of data is defined by, 10 – 90 Percentile Range
Statistical analysis often uses probability distributions