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Nina Tahhan, Eric Papas, Timothy R. Fricke, Kevin D. Frick, Brien A. Holden; Reliability of Ophthalmic Utility Measures. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1420.
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© ARVO (1962-2015); The Authors (2016-present)
Utilities are indices derived from quality of life (QoL) questionnaires and used in health economic analysis. Utilities have been derived for a variety of ocular conditions using various methods. The relative reliability of these methods is unclear. This study evaluates and compares the test-retest reliability of 3 methods.
Thirty-three subjects aged 21-34yrs with corrected Refractive Error (RE) underwent an eye exam and utility assessment on 2 occasions. Utility methods were Visual Analogue Scale (VAS) and two variants of Time Trade-Off (TTO). The TTO variations were in the remaining life years presented i.e. 10 years (TTO-10) or estimated years remaining (TTO-YR). Utilities were elicited for corrected and uncorrected RE. A repeated measures ANOVA with "methods" and "retest" as within subject factors was conducted.
Test and retest interval was 6 - 17 days. Mean spherical RE of the better eye was -3.15±2.79D. For corrected RE, mean difference in utility between test and retest groups was; VAS: 0.005±0.077; TTO-10: 0.007±0.029 and TTO-YR: 0.017±0.052. For uncorrected RE, mean difference was; VAS: 0.004±0.134, TTO-10: 0.015±0.134, TTO-YR: 0.017±0.129. No significant difference was observed between test and retest groups (p>0.05) and the difference was not dependant on the method used (p>0.05). The 95% limits of agreement for corrected and uncorrected RE respectively was; VAS: -0.15 to 0.16 and -0.28 to 0.27; TTO-10: -0.05 to 0.07 and -0.29 to 0.26; TTO-YR: -0.09 to 0.13 and -0.25 to 0.28.
The 3 methods show similar and acceptable reliability in this sample. All methods had better reliability with corrected vs uncorrected RE. When choosing a method other factors such as validity, responsiveness, time and ease of administration should be considered.
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