I have taken a performance measurement on a group of subjects, then put those subjects through a treatment, and remeasured their performance. I would like to comment on the similarity between the before vs after measurements. I have seen ICC used in this context but don't really understand what it's measuring because all explanations I have read about ICC refer to 'raters' which do not exist in my context.
I totally understand what a standard 1-way anova would give me in terms of testing a null hypothesis, it's the ICC that I am confused about. Could I get an explanation for its application when no 'raters' are involved?