Reliability

Inter-Rater Reliability

(consistency among scorers or observers). Independent judges observing the same behavior or reviewing the same assessment materials should come to the same general conclusions. High inter-rater reliability is important because it increases confidence that the procedure is really measuring what it is supposed to measure.

Test-Retest Reliability

A measure of consistency for tests and other instruments. Individuals are asked to take the test of interest and then take the same test again at a later date. The scores are then compared. The closer the scores are, the more reliable the test. Reliability is an important factor in testing because if paves the way for accuracy. Remember, reliability refers to a test producing consistent results, not necessarily valid results.

Internal Reliability

In a questionnaire designed to measure "potential alcoholism", for example, we expect that all the items on the questionnaire will contribute to identifying this potential. If some of the items are irrelevant, or if they do not meaningfully relate to the potential for alcoholism, they can reduce the internal reliability of the questionnaire and may skew the scores obtained on the questionnaire. This may lead to the erroneous indication that someone is at high risk for alcoholism when, in reality, they are not.