Intraclass Correlations using Mcgraw and Wong conventions defines 5 ICC´s for single scores.
I am interested in calculating both Two-way random, single measures, absolute agreement (Sometimes abbreviated as ICC 2.1A) and Two-way random, single measures, consistency (Sometimes abbreviated as ICC 2.1C).
Link to Wikipedia page with overview.
The first(ICC 2.1A) is easy as several packages (e.g. "irr", "rel", "psysch") support this:
Two-way random, single measures, absolute agreement (ICC 2.1A)
library(irr)
icc(ratings, model = c("twoway"),
type = c("agreement"),
unit = c("single"), r0 = 0, conf.level = 0.95)
But I am unsure about how to calculate the Two-way random, single measures, consistency. I read the package helpfiles as if the packages support Two-way mixed, single measures, consistency (ICC 3.1C), but not 2.1C.
That is, I think the below code gives me ICC 3.1C and not 2.1C
library(irr)
icc(ratings, model = c("twoway"),
type = c("consistency"),
unit = c("single"), r0 = 0, conf.level = 0.95)
Can anyone help me either find a package that calculates Two-way random, single measures, consistency or alternatively guide me on how to calculate it using a mixed model.
Best Answer
According to Which inter-rater equation should I use; ICC(2,1) or ICC(3,1)? and, as you pointed out, the McGraw and Wong article the results of ICC(2,1) and ICC(3,1) are the same. So the following code that you mentioned will give you ICC(2,1) and ICC(3,1) consistency: