Return to the Learning Resource College of Natural Resources
Statistics  
 

 

HOME
STATISTICS
LESSONS
CONTACT
HELP
 

 

 © 2007
 University of Idaho
 All rights reserved.

 Web Design - CTI

 

Lesson 3: Basic Descriptive Statistics
8 Calculating the Standard Deviation < Back | Next >
The formula for calculating the standard deviation is as follows:

S = √s2

It is simply the square root of the variance. The standard deviation is the most common measure of spread and is very useful in calculating many other statistics.

Example

If we continue with our tree density example we just used we could now calculate the standard deviation by taking the square root of 481. This would give us a standard deviation equal to 21.9.

Let’s use our last example to calculate the standard deviation.

Remember the following three data points are the flow rates for three streams in a given watershed in cubic feet per second: 106, 125, 202

The mean for the data is equal to 144.3 cubic feet per second, the variance is equal to 2544.4 and the number of samples is equal to 3

Which of the following is equal to the standard error?
A. 64.3
B. 50.4
C. 83.7
D. 48.9

Response:

LESSON 3
1 Overview
2 Intro to Descriptive Statistics
3 Calculating the Mean or Average
4 Calculating the Median
5 Calculating the Mode
6 Describing the Spread of Data
7 Calculating the Variance
8 Calculating the Standard Deviation
9 Graphical Representation of Data
10 The Stem and Leaf Plot
11 Review Questions
< Back | Next >

horizontal rule

HOME | STATISTICS | LESSONS | CONTACT | HELP