Jill wants to test the efficacy of a treatment versus a control group. Thus she wants to use a 2 arm design.
So far, we know that Jill is going to use a 2 arm design testing the effect of a treatment versus a control on prevention of a disease. Another important factor on sample size is the number of times Jill plans on measuring whether or not the disease has occurred. For example, is she going to test whether the disease has occurred only at the end of the study or at several time points throughout the study. How many times will you be measuring the response variable?
-- ErinEsp - 31 Jan 2010