Work out intraclass correlation instantly with clear inputs, formula shown and shareable results.
The intraclass correlation is the share of total variance attributable to genuine differences between subjects. Averaging across raters reduces the error term, which is why the average-rater ICC is always higher.
Single-rater ICC
ICC = σ²_between / (σ²_between + σ²_within)
Average-rater ICC
ICC = kσ²_between / (kσ²_between + σ²_within)
The single-rater ICC is 0.8 (good), rising to 0.923 for the average of three raters.
Below 0.5 is poor, 0.5 to 0.75 moderate, 0.75 to 0.9 good and above 0.9 excellent, following Koo and Li.