On 04/13/2012 04:17 AM, Bradley Carlson wrote:
Thanks for the tips everyone - I'll look into MCMC sampling for the CI. As
far as the power analysis goes, I'm somewhat familiar with the criticisms
regarding power analysis. I think this reviewer was curious about it
because there was a small sample size (small number of levels of the random
effect) and the ICC point estimate was not so low as to be biologically
insignificant. It would be nice to state in the paper how much larger of a
sample size would have enabled us to detect an effect given the observed
variation, as though this were a pilot study for planning a bigger
experiment. I'll certainly bring up the suggested citations, but I would
still be interested to know if there is a method available for performing a
power analysis for an LRT of a random effect. Thanks again,
I'd use simulation: you can write a function to simulate data and fit
the model to it, so you can run that for different sample sizes. It's
not too fiddly to write, and you can leave the computer to run it over
the weekend, so you can run reasonable sample sizes.
Bob
Brad
On Thu, Apr 12, 2012 at 12:18 PM, Brian Inouye<[email protected]> wrote:
In addition to Bob O'Hara's suggestion, here is another citation you can
give the reviewer/editor, as to why retrospective power analyses are a
waste of time.
Hoenig, J. M. and D. M. Heisey (2001). "The abuse of power: the pervasive
fallacy of power calculations for data analysis." American Statistician
55(1): 19 - 24.
Last year the ESA updated its author guidelines for reporting statistics,
and removed a suggestion to report power analyses that had been inserted in
the 1980s.
-Brian Inouye
Florida State University
Chair, statistical ecology section of the ESA
On 4/12/2012 6:00 AM,
r-sig-ecology-request@r-**project.org<[email protected]>wrote:
2) A reviewer requested a power analysis of the ability to detect a
significant random effect. Any tips on how to approach that?
Report the random effect and confidence intervals. Retrospective power
analyses are pretty pointless (e.g. see http://beheco.oxfordjournals.**
org/content/14/3/446.full<http://beheco.oxfordjournals.org/content/14/3/446.full>),
unless you're planning to repeat the experiment. Bob
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Bob O'Hara
Biodiversity and Climate Research Centre
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Germany
Tel: +49 69 798 40226
Mobile: +49 1515 888 5440
WWW: http://www.bik-f.de/root/index.php?page_id=219
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