What Is Test Reliability?
Reliability is the degree to which an assessment tool produces stable and consistent results. Even if the same subject takes a test more than once over a period of time, a reliable test will yield similar results.
Reliability has sub-types that must be satisfied
Parallel-Forms Reliability – To check for reliability using this technique, a test is divided into two forms. If the questions on both forms are answered in similar ways, then parallel-forms reliability is demonstrated.
Internal Consistency Reliability – This is used to assess the internal reliability between items. For example, a personality test may seem to have two or more questions that are asking the same thing. If the participant does in fact answer them in the same way, then internal consistency reliability can be assumed.
Inter-Rater Reliability – If two individuals rate a behavior on a test in the same way, then a test’s inter-rater reliability is confirmed.
Test-Retest Reliability – This is achieved by giving the same test at two different times and gaining the same results each time.
There are at least minor defects in nearly every test. Also, individuals taking a test may have different thoughts or feelings from one day to the next. There are factors that contribute to consistency, and factors that contribute to inconsistency. Consistency is attributed to stable traits or characteristics in an individual taking the test; height and weight, for example. Inconsistency is attributed to such things as the participant’s health on test day, their understanding of the test, or their luck in guessing a correct answer.
Why Is Reliability Important?
The reliability of a test is important because there is no point in having a test if it will yield different answers each time it’s used. This is especially true when the test is used to influence such the decisions as a client’s mental health diagnosis or their progress in psychotherapy.