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Jun 23, 2011

Sample Size and Power for Testing Two Variances

This add-in will estimate either the sample size or the power for testing two variances as an F-ratio. It is designed to work like the sample size and power calculators available through the JMP DOE menu.


The initial window includes a default significance level. Enter two standard deviations that represent the minimum difference that is important. Std Dev 1 represents the control population and Std Dev 2 represents the treatment population. Finally, enter either the sample size to estimate the power or the power to estimate the sample size and click Continue.

Note that this version provides the result for a balanced design. That is, both groups have the same size and the value entered or returned here is the total sample size or twice the size of each group. For example, if you enter 50, then the computation assigns 25 to each group.

The default test is two-sided for any difference. You may select either the lower or upper one-sided test instead. Be sure to enter the standard deviation values in the correct order.

For example, a confirmation is planned to demonstrate that recent improvements have reduced variation for an original standard deviation of 3 down to 2 based on a lower one-sided test with 90% power. The result is shown here:


Please note that I replaced the add-in after fixing a bug. If you have trouble estimating the power, then download the update and re-install.


why does the link above for download not open?


I just tried it and it worked without any problem. Are you logged in? Do you get an error message?



I'm sorry you're having trouble. When you click the link above your browser should download a .jmpaddin file. 


When you double click on the .jmpaddin JMP should open and prompt you to ask if you want to install the add-in.

Parallels DesktopScreenSnapz019.png



After you install it you'll find the menu option in your Add-Ins menu.


Parallels DesktopScreenSnapz020.png


If these steps don't help, post back and let me know where you're running into trouble and I'll try to assist further.


When I first tried this add-in, It worked, but it didn't make it into the add-ins menu.  


I've just re-downloaded the addin and it installed as described above.  



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