[R] shrout & fleiss ICC´s with varying numbers of judges

From: Helter Two <heltertwo_at_care2.com>
Date: Wed, 16 Jun 2010 13:32:01 -0700

Win7, R2.11.0

I am working on a report together with several co-authors. The data concern several performance measures on a set of groups. These measures are scored by external judges. We report findings on several datasets, including several of the 6 ICC's discussed by Shrout & Fleiss (1979). We determine these using the icc function from the irr package. We have also used the ICC function from the psych package.

However, one of the datasets has varying numbers of judges for each group. One group may be rated by 2 judges, whereas others may even have ratings by up to 5 judges. My problem is that I don't see how I can use the icc or ICC functions for determining the icc's these groups, since icc/ICC require that all groups have the same number of judges (as far as I understand). Alternatively, I could report the ICC1 and ICC2 (in the multilevel package), but these are different from the Shrout & Fleiss ones, and we would like to be consistent. (of course, I know that not all 6 icc's apply in every case, but we would like to stay within the Shrout & Fleiss framework and then report the relevant icc). I have searched extensively for a function that would allow to calculate S&F icc's for a varying number of judges, but I can't find one. Are there any there functions that allow me to do this? Or is there a way to still use icc or ICC?

thanks,
Peter Verbeet

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