Intraclass correlation coefficients: clearing the air, extending some cautions, and making some requests.

Intraclass correlation coefficients (ICCs) are frequently employed in health science research, often to assess intrarater and interrater reliability. In many cases, insufficient details are provided about these ICCs and there seem to be misunderstandings about their selection and how they should be interpreted. This paper is intended primarily to provide a clear, accessible description of ICCs, including how they should be selected, interpreted, and reported. Emphasis is given to areas where researchers seem to encounter the greatest conceptual difficulties and to exhibit the greatest misconceptions. Two extended examples are used to support the points being made. Major additional aims of this paper are to raise the awareness of authors, reviewers, and editors concerning the importance of using appropriate ICCs, and to encourage them to ensure that complete and accurate information about ICCs is reported in journal articles. Failure to do so perpetuates a risk that incorrect decisions might be made about matters that are of crucial importance for people's health. [ABSTRACT FROM AUTHOR]