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Re: st: clogit data format

From   Margaret R Grove <margaret.r.grove@Dartmouth.EDU>
Subject   Re: st: clogit data format
Date   Fri, 21 Mar 2008 09:44:44 -0400

We did the kappa analysis on the data before we dichotomized it and then used Stata's "kap" to compare pairs using a bootstrapped sample so the N isn't comparable.


Cathy L. Antonakos wrote:

With a kappa analysis, which Margaret wrote she had done, wouldn't the kappa also be undefined in the case of no variance between raters? I've just run across this issue in an analysis of multiple raters. It seems the kappa analysis should also have failed for other than the 290 cases with variance, so the N for the clogit would not have been a surprise. Cathy ---

Subject: Re: st: clogit data format

Thanks, Nick!

I was asked to do a clogit but will summarize as you suggested and see where that leads.


Nick Cox wrote:

If I understand this correctly, individuals for whom all raters agree
cannot be included in a -clogit- analysis. That seems to rule it out absolutely

as a way of examining the structure of agreement and disagreement.
There are many ways to look at the data, depending on what data
generation process
you have in mind. It's not clear to me that a binary response inescapably implies a logit analysis. Missings aside, four
for each individual imply that your data can be collapsed with loss of information to a table of the frequencies of 16 joint outcomes:
which may allow structure to be discerned. Here "0000" means all four
assign "0", and so forth.
Margaret R Grove

To clarify further where I think the problem may lie:

PHREG output notes "Number of Observations Read 2300" and "Number of Observations Used 2000" (300 have missing values for the dependent variable)

CLOGIT notes that 1710 observations (496 groups) were dropped because of

all negative or all positive outcomes and our final number of observations is 290!

With this I wonder if comparing the two methods makes sense and which method (PHREG or CLOGIT) is preferable (if any)?

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