What is Dispersion? An extract from the book "Practical Business Analytics using SAS"

Practical Business Analytics Using SAS: A Hands-on Guide: What is Dispersion? An extract from the book "Prac...:

What is Dispersion

Dispersion is the variation in data—the non uniformity or inconsistency in the values of a variable. The measures of dispersion indicate nothing about the middle value of the data. Rather, they give you an idea about the spread in the data. Dispersion can be measured using Range, Variance and Standard Deviation.

Anderson Wants to Cross a River 

Mr. Anderson, who can’t swim, wants to cross a small waterway. He asked a neighbor to describe the depth of that river, and the neighbor said its depth is 4 feet on average. Mr. Anderson is happy and starts to cross it. His happiness does not last long. The reason is that although the average is 4 feet, the depth at some places might have been 7 feet, which is more than Mr. Anderson’s height. If he had inquired about the deviation from average depth or the inconsistency of depth at various points, or at least the range of depth(minimum and maximum depeth) apart from the average depth of the river, it would have saved Mr. Anderson from drowning.

Therefore, merely knowing the average or the center value may not be sufficient in all cases. The deviation from center (or the dispersion) or the spread of a variable is also important. Given next are a few measures of dispersion.