"CHIDLOW Agnieszka" <[email protected]> wrote:
Please forgive me if you find this request silly (or basic), but I
have been having some nightmares to figure out how to use ex post
"fpower" for anova.
I have read about the power analysis (e.g. papers, and on
www.ats.ucla.edu), but it looks like I can't do the test because I
don't seem to know how to calculate delta and/or means for my groups.
Hence would really appreciate some help from you.
My anova results are:
(...)
---------------------------------------------
"Martin Weiss" <[email protected]> replied:
Seems from the explanations at
http://www.ats.ucla.edu/stat/stata/dae/fpower.htm that these values
are mere educated guesses, not results of calculations...
----------------------------------------------
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
use.
--
Phil Ender
Statistical Consulting Group
UCLA Academic Technology Services
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
