Intraclass correlation coefficients | Order |
Stata's new icc can measure absolute agreement and consistency of agreement.
Consider a dataset containing 24 ratings of 6 targets by 4 judges. Assume that a different set of four judges is used to rate each target so that we have a one-way random-effects model.
We can estimate the correlation of ratings made on the same targets by typing
. icc rating target Intraclass correlations One-way random-effects model Absolute agreement Random effects: target Number of targets = 6 Number of raters = 4
rating | ICC [95% Conf. Interval] | |
Individual | .1657418 -.1329323 .7225601 | |
Average | .4427971 -.8844422 .9124154 | |
The correlation of measurements made on the same individual is 0.1657.
The correlation among mean ratings for each team of judges is 0.4428. The average ICC can be used when teams of different raters are used to rate a target. Teams of physicians are sometimes evaluated in this manner.
Now let's pretend the same team of judges rated each target. If the judges were drawn randomly from the population, then we would have a two-way random-effects model. We can estimate the correlations by typing
. icc rating target judge Intraclass correlations Two-way random-effects model Absolute agreement Random effects: target Number of targets = 6 Random effects: judge Number of raters = 4
rating | ICC [95% Conf. Interval] | |
Individual | .2897638 .0187865 .7610844 | |
Average | .6200505 .0711368 .927232 | |
The correlation of measurements made on the same individual is 0.2898.
The correlation among mean team ratings with those that might be produced by another team is 0.6201.
Finally, suppose the four judges are the only judges of interest. Judge is now a fixed effect in the model, and we have a two-way mixed-effects model. We can obtain the correlations by typing
. icc rating target judge, mixed Intraclass correlations Two-way mixed-effects model Consistency of agreement Random effects: target Number of targets = 6 Fixed effects: judge Number of raters = 4
rating | ICC [95% Conf. Interval] | |
Individual | .7148407 .3424648 .9458583 | |
Average | .9093155 .6756747 .9858917 | |
See the manual entry.
See New in Stata 18 to learn about what was added in Stata 18.