**Guide for
Determining the Confidence Interval Using Excel**

1. Click in another empty cell.

2. Click the Function icon.

3. Scroll and choose Confidence. Click "OK."

The following dialogue box will appear.

4. In the box labeled **Alpha, **insert the Alpha level you wish to use in
your analysis (For example, .05 for a 95% confidence interval).

5. Click in the box labeled **Standard_dev** and type in the value computed in
the STDEV function performed above.

6. In the box labeled **Size**, insert the number of data points in the
sample.

7. Click OK, and the confidence interval will be computed.

8. Add and subtract the confidence interval value from the mean found above to find the confidence interval range.

Original work on this document was done by Central Virginia Governor's School students Jennifer Rice, Eliza Evans, and Chris Earle (Class of '03).

Copyright © 2002 Central Virginia Governor's School for Science and Technology, Lynchburg, VA