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Date:         Mon, 5 Oct 2009 06:36:23 -0700
Reply-To:     "cat.." <cat.b41@GMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "cat.." <cat.b41@GMAIL.COM>
Organization: http://groups.google.com
Subject:      Appropriate model for intra-class correlation coefficient
              calculation ?
Comments: To: sas-l@uga.edu
Content-Type: text/plain; charset=ISO-8859-1

Hi folks !

In a pediatric clinical trial, I have 2 scales that measure the same quantity (let's call it Y) on each child in the trial: One based on a questionnaire filled in by the child him/herself, the second one based on a questionnaire filled in by his/her parent.

I need to calculate the Intra-class correlation coefficient between these two scores (parent-rated versus patient-rated) to measure their agreement.

That papers gives several formula, each being based on an ANOVA model that fits the score variability on several sources of variability.

http://www3.uta.edu/faculty/ricard/COED/McGraw%20(1996)%20Forming%20inferences%20about%20ICCs.pdf

The paper gives a speific ICC formula (with 95% CIs) for each of the models beneath:

1 - Score = overall mean + random patient effect + error 2 - Score = overall mean + random patient effect + random rater effect + interaction patient*rater + error 2a- Score = overall mean + random patient effect + random rater effect + error 3 - Score = overall mean + random patient effect + fixed rater effect + interaction patient*rater + error 3a - Score = overall mean + random patient effect + fixed rater effect + error.

I'm not sure what the model is that best fits my data and would like your thought about it.

In fact, I'd go for the 3a one but the problem I have is that the rater and the patient are not independant as the rater is either the patient him/herself, or her/his parent. So, none of these models would be valid.

Thanks for your input, especially if you have experience in this.

Cheers,

Catherine.


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