Test-retest reliability

Test-retest reliability is a measure of the reproducibility of the scale used within a patient-reported outcome measure (PROM); i.e. it is the ability for a PROM to provide consistent scores over time in a stable population. In an experiment with multiple time points, the expectation is that the measurement tool chosen could consistently reproduce the same result providing all other variables remain the same. Tools that do provide such consistency are regarded as having high test-retest reliability and, therefore, appropriate for use in longitudinal research. The reliability scores can be calculated by understanding the magnitude of the relationship between test statistics and, thus, the correlation coefficient (r) is calculated. A measure providing the same output at every time point would deliver a perfect linear correlation of r = 1.