Dispersion is a statistical calculation that allows you to tell how far apart your data is spread. Many different ways are available to calculate dispersion, but two of the best are the range and the average deviation. The range is the difference between the highest and lowest value of your statistics. Your average deviation looks at your mean and how each data point differs from the mean.
Range
Find your data's lowest number. For example, assume the lowest value is 4.
Find your data's highest value. In the example, assume the highest is 10.
Subtract the lowest value from the highest value to calculate range. In the example, the range is 10 minus 4, which equals 6.
Average Deviation
Calculate your average by adding up all your data values and divide by the number of data values. For example, assume your data values are 4, 8 and 10. Then, 4 plus 7 plus 10 equals 22. Finally, 22 divided by 3 equals an average of 7.33.
Subtract your values from the average. If the number is a negative, then drop the negative sign. In the example, 10 minus 7.33 equals 2.66, 7 minus 7.33 equals -0.33 and 4 minus 7.33 equals -3.33. So you have 2.66, 0.33 and 3.33. These are your differences from the mean.
Add together your differences from the mean and divide by the number of data values you have. In the example, 2.66 plus 0.33 plus 3.33 equals 6.32. Then, 6.32 divided by 3 equals an average deviation of 2.106.
References
About the Author
Carter McBride started writing in 2007 with CMBA's IP section. He has written for Bureau of National Affairs, Inc and various websites. He received a CALI Award for The Actual Impact of MasterCard's Initial Public Offering in 2008. McBride is an attorney with a Juris Doctor from Case Western Reserve University and a Master of Science in accounting from the University of Connecticut.