Reliability coefficient

Definition
noun
(statistics) A quantitative expression of the reliability or consistency in the measurement of test scores, for example, in test-retest reliability, or in equivalent-form reliability.
Supplement
The symbol for reliability coefficient is letter r. A reliability value of 0.00 means absence of reliability whereas value of 1.00 means perfect reliability. An acceptable reliability coefficient must not be below 0.90, less than this value indicates inadequate reliability. For instance, r =.90 on a test means that 90% of the test score is accurate while the remaining 10% consists of standard error. If the r=0.6, it means that only 60% of the test score is reliable and the other 40% may be caused by an error.
Thus, the higher the reliability coefficient is, the lower the standard error is. The lower the standard error is, the more reliable the test scores are.
See also: test-retest reliability, equivalent-form reliability.