ICC {psych} | R Documentation |
The Intraclass correlation is used as a measure of association when studying the reliability of raters. Shrout and Fleiss (1979) outline 6 different estimates, that depend upon the particular experimental design. All are implemented.
ICC(x,digits=2)
x |
a matrix or dataframe of ratings |
digits |
Round the output to digits |
Shrout and Fleiss (1979) consider six cases of reliability of ratings done by k raters on n targets.
1) Each target is rated by a different set of k judges. 2) A random sample of k judges rate each target 3) A fixed set of k judges rate each target. Then, for each of these cases, is reliability to be estimated for a single rating or for the average of k ratings? (The 1 rating case is equivalent to the average intercorrelation, the k rating case to the Spearman Brown adjusted reliability.
ICC1 |
Intraclass correlation for different judges |
ICC2 |
Intraclass corelation for the same random judges |
ICC3 |
Intraclass corelation for the same fixed judges |
ICC12 |
Intraclass corelation for the average of different judges |
ICC22 |
Intraclass corelation for the average of random judges |
ICC3 |
Intraclass corelation for the average of fixed judges |
William Revelle
Shrout, Patrick E. and Fleiss, Joseph L. Intraclass correlations: uses in assessing rater reliability. Psychological Bulletin, 1979, 86, 420-3428.
Revelle, W. (in prep) An introduction to psychometric theory with applications in R. Springer.
ICC(attitude)