Question

What is the difference between ICC (A,J) and ICC (A,K)? Can you use both to compare reliability of your data set?

Answer 1

Intraclass correlation coefficient (ICC) is a widely used reliability index in test-retest, intrarater, and interrater reliability analyses. Reliability is defined as the extent to which measurements can be replicated.

There are different forms of ICC that can give different results when applied to the same set of data, and the ways for reporting ICC may vary between researchers. Given that different forms of ICC involve distinct assumptions in their calculations and will lead to different interpretations, it is important that researchers are aware of the correct application of each form of ICC, use the appropriate form in their analyses, and accurately report the form they used.

There are 10 forms of ICCs. Because each form involves distinct assumptions in their calculation and will lead to different interpretations, researchers should explicitly specify the ICC form they used in their calculation. A thorough review of the research design is needed in selecting the appropriate form of ICC to evaluate reliability. The best practice of reporting ICC should include software information, “model,” “type,” and “definition” selections.

Therefore, both forms may be used to assess the reliability.