Assessing Reliability and Precision of Measurement: An Introduction to Intraclass Correlation and Standard Error of Measurement

The reliability and precision of measurement in sports medicine are of concern in both research and clinical practice. The validity of conclusions drawn from a research project and the rationale for decisions made about the care of an injured athlete are directly related to the precision of measurement. Through analysis of variance, estimates of reliability and precision of measurement can be quantified. The purpose of this manuscript is to introduce the concepts of intraclass correlation as an estimate of reliability and standard error of measurement as an estimate of precision. The need for a standardized set of formulas for intraclass correlation is demonstrated, and it is urged that the standard error of measurement be included when estimates of reliability are reported. In addition, three examples are provided to illustrate important concepts and familiarize the reader with the process of calculating these estimates of reliability and precision of measurement.