psych (version 1.0-58)

ICC: Intraclass Correlations (ICC1, ICC2, ICC3 from Shrout and Fleiss)

Description

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.

Usage

ICC(x,digits=2)

Arguments

x

a matrix or dataframe of ratings

digits

Round the output to digits

Value

• 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

Details

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.

References

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.

Examples

ICC(attitude)