A measure of consistency obtained by administering the same test to the same group of people at two different times and correlating the scores. High test-retest reliability indicates that the measure produces stable results over time.
Developed in early 20th-century psychometrics as researchers needed to demonstrate that their tests measured stable traits rather than temporary states. The hyphenated 'test-retest' format emphasizes the temporal aspect of this reliability assessment.
If your IQ test gives you a score of 120 today and 85 next week, it has terrible test-retest reliability! This type of reliability assumes the trait being measured is actually stable over time—which isn't always true.
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