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st: fpower

From   "CHIDLOW Agnieszka" <>
To   <>
Subject   st: fpower
Date   Mon, 22 Jun 2009 00:25:48 +0100

Dear Phil,
Thank you very much for your e-mail and suggestions regarding fpower and anove (you are absolutely right, thanks for that). 
If I can ask, why would you run "simpower nm year, reps(2000)" using 2000?
Once again, many thanks

There certainly are educated guesses involved in any power analysis.
In the case of -fpower- the main educated guess is concerning the
delta().  After that -fpower- computes power based on the noncentral
F-distribution.  So there are indeed calculations going on.  The
-simpower- program generates random samples with given means and
standard deviations and computes power by counting the number of
significant results.  I usually suggest at least 1,000 iterations.

As for Agnieszka power question, I would recommend running the
following: "simpower nm year, reps(2000)"

I'm a little confused by the statement that nm is 2 groups.  Does this
mean that there is a categorical response variable?  If so, then
-anova- is the wrong tool to

Phil Ender
Statistical Consulting Group
UCLA  Academic Technology Services
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