"Piface" the cow, by Brian Lenth Java applets for power and sample size
Select the analysis to be used in your study:

This software is intended to be useful in planning statistical studies.  It is not intended to be used for analysis of data that have already been collected.

Each selection provides a graphical interface for studying the power of one or more tests.  They include sliders (convertible to number-entry fields) for varying parameters, and a simple provision for graphing one variable against another.

Each dialog window also offers a Help menu.  Please read the Help menus before contacting me with questions.

The "Balanced ANOVA" selection provides another dialog with a list of several popular experimental designs, plus a provision for specifying your own model.

Note: The dialogs open in separate windows. If you're running this on an Apple Macintosh, the applets' menus are added to the screen menubar -- so, for example, you'll have two "Help" menus there!

You may also download this software to run it on your own PC.

Note: These require a web browser capable of running Java applets (version 1.1 or higher). If you do not see a selection list above, chances are that you either have disabled Java, your browser is not new enough., or you need to download a JRE plug-in from java.sun.com.  Due to a compatibility bug, many plug-ins size the applet window before allowing for an additional strip with a security warning.; drag the bottom of the window downward a bit to compensate.

Citing this software

If you use this software in preparing a research paper, grant proposal, or other prublication, I would appreciate your acknowledging it by citing it in the references.  Here is a suggested bibliography entry in APA or "author (date)" style:

Lenth, R. V. (2006).  Java Applets for Power and Sample Size [Computer software].  Retrieved month day, year, from http://www.stat.uiowa.edu/~rlenth/Power.

This form of the citation is appropriate whether you run it online (give the date you ran it) or the stand-alone version (give the date you downloaded it).

Download to run locally

The file piface.jar may be downloaded so that you can run these applications locally.  [Note: Some mail software (that thinks it is smarter than you) renames this file piface.zip.  If this happens, simply rename it piface.jar; do not unzip the file.]  You may also want the icon file piface.ico if you put it on your desktop or a toolbar.  You will need to have the Java Runtime Environment (JRE) or the Java Development Kit (JDK) installed on your system.  You probably already have it; but if not, these are available for free download for several platforms from Sun.  If you have JDK or JRE version 1.2 or later, then you can probably run the application just by double-clicking on piface.jar.  Otherwise, you may run it from the command line in a terminal or DOS window, using a command like

    java -jar piface.jar

This will bring up a selector list similar to the one in this web page.  A particular dialog can also be run directly from the command line, if you know its name (can be discovered by browsing piface.jar with a zip file utility such as WinZip).  For example, the two-sample t-test dialog may be run using

java -cp piface.jar rvl.piface.apps.TwoTGUI


This software is made available as-is, with no guarantees; use it at your own risk.  I welcome comments on bugs, additional capabilities you'd like to see, etc.  I am also willing to provide minimal support if you truly don't understand what inputs are required.  However, each applet has a help menu, and I do request that you carefully read that before you e-mail me with questions. 

If you need statistical advice on your research problem, you should contact a statistical consultant; and if you want expert advice, you should expect to pay for it.  Most universities with statistics departments or statistics programs also offer a consulting service.  If you think your research is important, then it is also important to get good advice on the statistical design (i.e., before you start collecting data) and analysis.

If you have carefully read the above two paragraphs, and still find it appropriate to contact me, my e-mail address is russell-lenth@uiowa.edu.


Here are two very wrong things that people try to do with my software:
Here are three very right things you can do:
Many funding agencies require a power/sample-size section in grant proposals.  Following the above guidelines is good for improving your chances of being funded.  You will have established that you have thought through the scientific issues, that your procedures are sound, and that you have a defensible sample size based on realistic variance estimates and scientifically tenable effect-size goals. 

To read more, please see the following references:


Links to other sites

It is not unlikely that one or more of these links is broken.  If that happens, please let me know (especially if you can correct it!)

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