Power / Sample Size Calculations for a Balanced ANOVA

How many factors are there?
(e.g., 3 for a three-way ANOVA)

How many levels are there?
(e.g., 3 2 2 for a 3x2x2 ANOVA. There must be a total of 25 or fewer levels.)

How many replicates are there per factor combination?
(e.g., to have 5 replicates in a 3x2x2 ANOVA, a total of 5x3x2x2 specimens would be required.)

For tests of which factor do you want to estimate power values?
(e.g., if the experiment were a 5x2x4 ANOVA and you were interested in a test for a difference in the 4 levels of factor three, you would choose 3.)

What are the hypothesized means as a fraction of the overall mean?
(For example, if there are five levels for the factor, and you expect that level 1 will yield a mean that is about 80% of the overall average, that levels 2, 3, and 4 will yield means that are approximately equal to the overall average, and level 5 will yield a mean that is about 120% of the overall average, then your response should be .8 1 1 1 1.2)

How many coefficients of variation do you want to consider?

What are they?
(e.g., .25 if the standard deviation of the response population is approximately 25% of its mean)

What power do you wish to achieve?
(e.g., .90 if you want to have a 90% chance of obtaining a statistically significant result given that the difference actually exists. Desired power values must lie between 0 and 1.)

What name do you want for your results file?

The name should be unique to you to prevent the file from being accidentally overwritten by another user.

Since you will see an html document that presents the results as soon as you execute the program, you may not want an ascii copy. However, we do provide this option.

The ascii file will be written in the pub/tt anonymous ftp directory. If a file by the same name already exists in the directory, the new results will be appended to the existing file. Check the anonymous ftp link for directions about retrieving the file.

If ftp does not run on your machine, e-mail me at sverrill@fs.fed.us and ask me to e-mail the results file to you. Do this quickly as the pub/tt directory is cleaned weekly.

For further information, please contact Steve Verrill at sverrill@fs.fed.us or 608-231-9375.
Last modified on 1/12/97.