Posted by
Rich Ulrich on
Mar 10, 2011; 11:28pm
URL: http://spssx-discussion.165.s1.nabble.com/Why-is-95-CI-for-ICC-so-large-tp3422764p3424342.html
The main difference between a simple ICC and a Pearson R is that
the ICC *assumes* that the means are the same. The result is a
smaller value for the ICC than for the Pearson when the means differ.
I expect that your ICC for the depressed group has a wider CI
because of an underlying mean difference, since that is the only
potential difference I can think of, to account for the discrepancy.
The N's are actually larger for the depressed group, which would
tend to give a smaller CI. Otherwise -- Are you sure that all the
data were included in the analysis, nothing Missing?
With two raters, I prefer to look at SPSS's paired t-test between raters.
That shows me both the mean difference and the direct correlation.
--
Rich Ulrich
----------------------------------------
> Date: Wed, 9 Mar 2011 20:53:52 -0800
> From:
[hidden email]
> Subject: Why is 95% CI for ICC so large?
> To:
[hidden email]
>
> Hi,
> I have run ICC's with a 95% CI to compare agreement self reported rating
> by the patient and the doctor's rating by another characteristic. For
> example, I divided the sample between the patient's who had major
> depression and those without major depression and determined the
> agreement of the MD's with patients with major depression and separately
> agreement with patient's without major depression.
> The ICC for those without depression (n=153) was 0.43 (95%CI 0.23, 0.52
> ) and for those with depression (n=224) it was 0.43 (CI 0.04, 0.66).
> Why is the CI for the second group so much wider than for the first? The
> ICC syntax I am using is /ICC=model (random) type(absolute).
> Thanks for any help,
> Jan
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