```Date: Mon, 5 Oct 2009 06:36:23 -0700 Reply-To: "cat.." Sender: "SAS(r) Discussion" From: "cat.." 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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