Some other papers on this topic:
Goodman SN, Berlin JA. The use of predicted confidence intervals when
planning experiments and the misuse of power when interpreting
results. Ann Intern Med 1994;121:200-6. Erratum in: Ann Intern Med
1995;122:478.
Thomas L. Retrospective power analysis. Conservation Biology 1997;11:276-280.
Yuan K-H, Maxwell S. On the post hoc power in testing mean
differences. Journal of Educational and Behavioral Statistics 2005;30.141-167.
Walters SJ. Consultants' forum: should post hoc sample size
calculations be done? Pharm Stat 2008 Apr 17 Epub
I believe all of these argue against such post hoc calculations.
Doug
At 13:56 10/10/2008, Neil Shephard wrote:
>Personally I despise post-hoc power calculations, they're pointless
>and do nothing to enlighten the results of your test.
>
>Its like trying to tell someone who's just won the lottery that they
>shouldn't buy lottery tickets as the probability of winning is low.
>They don't care, they've already got their result (and were fortunate
>enough to have won that time)!
>
>A couple of papers on this are...
>
>Hoenig, John M. and Heisey, Dennis M. (2001), The Abuse of Power: The
>Pervasive Fallacy of Power Calculations for Data Analysis The American
>Statistician, 55, 19-24.
>
>Levine M, Ensom MH (2001) Post hoc power analysis: an idea whose time
>has passed? Pharmacotherapy 21.4:405-409
>
>I'm sure there are more references out there.
>
>The only purpose they serve is to inform the researcher about an
>appropriate sample size for their next study.
>
>Neil
>--
>"We should make things as simple as possible, but not simpler." -
>Anon (not Albert Einstein)
>
>Email - [log in to unmask]
>Website - http://slack.ser.man.ac.uk/
>Photos - http://www.flickr.com/photos/slackline/
_____________________________________________________
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Doug Altman
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