Understanding the standard deviation

The standard deviation is "the amount a typical score differs from the mean."
So estimate the mean and then estimate about how far out you have to go from there to capture about half the scores.

Be able to estimate the standard deviation

• Estimate stdev from a graph |

(Easier: Train your eye to estimate the standard deviation from a graph. This applet has the correct answer in the middle each time. Just run through several of those and see that you are looking for the length of the bar away from the center to go out to a bit more than half the scores on that side.)

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Additional useful visualizations:

Since you are thinking about how far the scores are from the mean, it is useful to be able to quickly see how far each score is from the mean.

Useful to check your work:

Compute the standard deviation of data: Use the applet that computes statistics and ask it for the standard deviation.

Useful to see why you DON'T really want to compute a standard deviation by hand!

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