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st: Problem Generating ICC Using xtmixed


From   Dylan Galos <galos002@umn.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: Problem Generating ICC Using xtmixed
Date   Fri, 11 Jan 2013 15:47:11 -0600

I'm using xtmixed (using the item as the dependent variable and the subject as the group variablle) and the postestimation estat icc to calculate ICCs for a test-retest reliability study of several Likert-type items. For only one item, the LR test (vs linear regression) had a chibar2 value of 0, p = 1, and the icc failed to calculate with error r(498) and the error message "Maximum number of iterations exceeded" (the xtmixed model itself took 3 iterations to converge). As I looked through the data, the responses changed between time1 and time2 for many of these subjects (it's probably unreliable), only in this one item, and I'm not sure what a valid next approach would be to estimate this, or how to interpret this result/error.

If it helps, my syntax was:

xtmixed var || surveyid:, mle
estat icc

Thank you for your help.

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