A calculated number whose value must be between 0 and 1. The number describes the consistency of the assessment results. The larger the number's magnitude, the more consistent the assessment. For example, if the coefficient value were 1, all students' scores would be expected to rank exactly the same way on retesting.
Joint Committee on Standards for Educational Evaluation. (2003). The Student Evaluation Standards, Thousand Oaks, CA: Corwin Press.