The Range Rule of Thumb says that the range is about four times the standard deviation. The standard deviation is another measure of spread in statistics. It tells you how your data is clustered around the mean.

Formula

s≈R4s≈R4

Where −

·         ss = standard deviation.

·         RR = Maximum – Minimum of a range.

How the range rule works, we will look at the following example.

Example

Problem Statement:

Given the following values: 12, 12, 14, 15, 16, 18, 18, 20, 20, and 25. Calculate standard deviation using range rule of thumb.

Solution:

These values have mean of 17. we first calculate the range of our data as 25 – 12 = 13, and then divide this number by four we have our estimate of the standard deviation as 134=3.25134=3.25. This number is relatively close to the true standard deviation, and good for a rough estimate.