In the context of reliability, what does 'test-retest' measure?

Test-retest reliability is a fundamental concept in psychological and educational measurement that assesses the stability of test scores over time. When a test is administered to the same group of individuals at two different points in time, and the scores are compared, it reflects how consistent the results are when no change has occurred in the underlying construct being measured. High test-retest reliability indicates that the test produces similar outcomes on repeated applications, suggesting that the measure is stable across time, which is vital for assessing traits or constructs that are expected to remain constant.

This concept is essential because it validates the test as a reliable tool—indicating that the observed scores are not merely a function of random variability or situational factors at the time of testing. Thus, test-retest reliability is crucial for establishing the dependability of psychological tests, educational assessments, and various other metrics that rely on consistency over time.