Geometric standard deviation

Geometric standard deviation is a measure of how spread out a group of numbers are. It is also called the spread. To find the geometric standard deviation, you start with a group of numbers like 1, 2, 4 and 10. To work out the spread, you first need to find their 'average', which is 4.5. Then, for each of the numbers in the group, you calculate how much it is bigger or smaller than the average. For example, 1 is 3.5 smaller than the average, 2 is 2.5 smaller, 4 is 0.5 smaller, and 10 is 5.5 bigger. After you have calculated this for each number, you take the "square root" of the product of all the numbers. The square root is a special number which, multiplied by itself, gives you the original number back. In this case, that number is 1.83. That number is the geometric standard deviation, and it tells you how spread out the group of numbers is.