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I'm hoping to do a study to calculate whether 1 method of measurement is more variable than another in a subgroup of patients.

I assume this will be done with an F-test, from some reading?

However, I'm unsure as to how to do a power calculation for this? Would I have to synthesize data and then repeatedly run an F-test to see if it's powered? That seems very dirty, but I can't see an appropriate function in R...

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    $\begingroup$ The F test for variance is usually not recommended because it's very sensitive to the normality assumption. $\endgroup$
    – Glen_b
    Commented Apr 16, 2015 at 15:37

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Following links are likely to help you:

From: http://en.wikipedia.org/wiki/Levene%27s_test

In statistics, Levene's test is an inferential statistic used to assess the equality of variances for a variable calculated for two or more groups.

And this page shows how to calculate power and sample size for Levene's test: http://gradworks.umi.com/14/47/1447667.html

Others:

http://www.stat.purdue.edu/~zhanghao/STAT514/handout/chapter03/PowerSampleSize.pdf

http://www.webpages.uidaho.edu/~chrisw/stat507/sccpow1.pdf

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    $\begingroup$ Link-only answers tend, sooner or later, to degrade through "link rot." At a minimum, please summarize the contents of your links so that when they disappear or change, your answer will still be useful. $\endgroup$
    – whuber ♦
    Commented Apr 17, 2015 at 17:27

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