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 ______________________________________________ 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.
