Standard deviation (variance when we square standard deviation)is a measurement of dispersion. It shows how far or how close the individual scores are from the mean (the middle of the bell curve) and from each other. If the scores are spread out far...we have a large standard deviation. If we have a small standard deviation, the scores are very close to each other.

Explain this simple example:

Scores of 5 students on a 20 point history test:

• Mike X = 12/20
• Paul X = 10/20
• Mike K. X = 15/20
• Jeff X = 17/20
• Tom X = 8/20

1st step: Find the mean score 12.4 (Xbar)

__

StudentScore (X)(X-X)(X-X)Squared

Mike12-.4.16

Paul10-2.45.76

Mike K.152.66.76

Jeff174.621.16

Tom8-4.419.36

E is sum053.20