Jill wants to test the efficacy of two treatments taken separately and also taken together. She will need to use a factorial design.
So far, we know that Jill is going to use a factorial design testing the effect of two treatments separately and when taken in conjunction on reducing the size of a tumor. Another important factor for determining sample size is the number of times Jill plans on measuring the size of the tumor. For example, is she only interested in the size of the tumor at the end of the study, or is she planning on measuring the tumor at several prespecified time points throughout the study. How many times will you be measuring the response variable?
-- ErinEsp - 31 Jan 2010