Test—retest reliability of the Arden Grating Test: inter‐tester variability

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Abstract
The aim of this study was to investigate the test‐retest reliability of the Arden Grating Test (AGT), and to assess the extent to which any variance in AGT score on retest can be attributed to intra‐subject and inter‐tester differences. Twelve patients with various patholgies and whose contrast sensitivity covered a wide range were each tested twice by six testers. It was shown that variance attributable to testing by different clinicians accounted for approximately 25% of the total variance, and that the 95% confidence limits about any observed score were ± 15 AGT units, which is about one quarter of the total dynamic range of the test. The large range of scores encompassed by the 95 % confidence limits represents considerable unreliability, the consequence of which is a high misclassification rate, i.e. many false positives and false negatives, especially in the context of primary vision screening for which it was designed.