#### Transcript of Stats - Lesson #4

**Lesson #4 - Standard Deviation**

What is Standard Deviation?

1. A measure of spread

2. Shows how much variation (dispersion) exists from the mean.

- A low standard deviation indicates that the data points tend to be very close to the mean.

3. The square root of the variance

Step 2

By hand once, calculator ever after...

The Way out

1. Put your data into a list on your calculator

2. In the Stats menu, go to calc and to one variable stats and find s. Voila!

Calculating Standard Deviation

A picture is worth a thousand words

On the left are two distributions with the same mean but different standard deviations. On the right are two distributions with the same standard deviation but different mean values.

Why is it divided by n-1?

http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1008&context=imseteach

What do you notice about these two graphs?

The standard deviation is NOT resistant because we are finding the average distance to the mean and the outliers are included in that calculation

Why divide by n-1 instead of n if we are finding the average?

Full transcript