Dear Anne
Can you resend the eror message which you accidentally sent only to me
please?
Michael
On 27/08/2019 08:02, CHATTON Anne wrote:
Dear Michael,
Thanks a lot for your suggestion. This is what I am trying to do with R
(longpower and gee packages). But I am getting stuck with a confusing error
message sent earlier I don't understand.
Best,
Anne
-----Message d'origine-----
De : Michael Dewey [mailto:li...@dewey.myzen.co.uk]
Envoyé : lundi, 26 août 2019 18:29
À : Marc Schwartz <marc_schwa...@me.com>; CHATTON Anne <anne.chat...@hcuge.ch>
Cc : R-help <r-help@r-project.org>
Objet : Re: [R] Code modification for post-hoc power
Dear Anne
In addition to Marc's comments if you are forced to do this then, assuming your
package computes sample size from power then just feed it a range of powers and
find the one for which it calculates the sample size you had. There is a more
elegant way to do this using uniroot but brute force should work.
Michael
On 26/08/2019 13:42, Marc Schwartz via R-help wrote:
On Aug 26, 2019, at 6:24 AM, CHATTON Anne via R-help <r-help@r-project.org>
wrote:
Hello everybody,
I am trying to accommodate the R codes provided by Donohue for sample size calculation in
the package "longpower" with lmmpower function to estimate the post-hoc power
(asked by a reviewer) of a binary GEE model with a three-way interaction (time x
condition x continuous predictor) given a fixed sample size. In other words instead of
the sample size I would like to estimate the power of my study.
Could anyone please help me to modify these codes as to obtain the power I'm
looking for.
I would really appreciate receiving any feedback on this subject.
Yours sincerely,
Anne
Hi,
Three comments:
1. Don't calculate post hoc power. Do a Google search and you will find a
plethora of papers and discussions on why not, including these:
The Abuse of Power: The Pervasive Fallacy of Power Calculations for Data
Analysis
The American Statistician, February 2001, Vol. 55, No. 1
https://www.vims.edu/people/hoenig_jm/pubs/hoenig2.pdf
Post Hoc Power: Tables and Commentary
https://stat.uiowa.edu/sites/stat.uiowa.edu/files/techrep/tr378.pdf
Observed power, and what to do if your editor asks for post-hoc power
analyses
http://daniellakens.blogspot.com/2014/12/observed-power-and-what-to-do
-if-your.html
Retraction Watch:
Statisticians clamor for retraction of paper by Harvard researchers they
say uses a “nonsense statistic”
https://retractionwatch.com/2019/06/19/statisticians-clamor-for-retrac
tion-of-paper-by-harvard-researchers-they-say-uses-a-nonsense-statisti
c/
PubPeer Comments on the paper cited in the above RW post:
https://pubpeer.com/publications/4399282A80691D9421B497E8316CF6
A discussion on Frank's Data Methods forum also related to the same paper
cited above:
"Observed Power" and other "Power" Issues
https://discourse.datamethods.org/t/observed-power-and-other-power-iss
ues/731/30
2. If you are still compelled (voluntarily or involuntarily), you may want to
review the vignette for the longpower package which may have some insights,
and/or contact the package maintainer for additional guidance on how to
structure the code. See the vignette here:
https://cran.r-project.org/web/packages/longpower/vignettes/longpower.
pdf
3. Don't calculate post hoc power.
Regards,
Marc Schwartz
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
---
This email has been checked for viruses by AVG.
https://www.avg.com
--
Michael
http://www.dewey.myzen.co.uk/home.html
--
Michael
http://www.dewey.myzen.co.uk/home.html
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
