# Standard Deviation

This is a great document on standard deviation. All information comes from 2 websites which are noted on the top of the document. Really helpful step by step explanation and example.

- Created by: Former Member
- Created on: 18-12-12 09:26

First 301 words of the document:

Compiled by Tilly

The information is all from 2 websites (asides from the summary). I have

copied it into this document so that you can obtain the method more simply.

This isn't actually my own work, but I found the following information very

useful.

Information from:

http://sonia.hubpages.com/hub/stddev

http://answers.yahoo.com/question/index?qid=20090521103304AAV1BoI

Standard Deviation is a measure of spread around a mean. The smaller the

Standard Deviation the closer the observations are clustered around the

mean.

First, you need to determine the mean. The mean of a list of numbers is the

sum of those numbers divided by the quantity of items in the list (add all the

numbers up and divide by how many there are).

Then, subtract the mean from every number to get the list of deviations.

Create a list of these numbers. It's OK to get negative numbers here. Next,

square the resulting list of numbers (read: multiply them with themselves).

Add up all of the resulting squares to get their total sum. Divide your result by

one less than the number of items in the list.

To get the standard deviation, just take the square root of the resulting

number

I know this sounds confusing, but just check out this example:

your list of numbers: 1, 3, 4, 6, 9, 19

mean: (1+3+4+6+9+19) / 6 = 42 / 6 = 7

list of deviations: 6, 4, 3, 1, 2, 12

squares of deviations: 36, 16, 9, 1, 4, 144

sum of deviations: 36+16+9+1+4+144 = 210

divided by one less than the number of items in the list: 210 / 5 = 42

square root of this number: square root (42) = about 6.48

Step by Step guide (summary)

1. Add all of the values together and divide by how many they are (mean).

## Comments

No comments have yet been made