Test–Retest Reliability of Health-Related Quality-of-Life Questionnaires in Adults with Strabismus
Accepted 1 November 2009. published online 08 February 2010. Corrected Proof
Purpose
To report the test–retest variability of two health-related quality-of-life instruments: the new Adult Strabismus 20 (AS-20) and the National Eye Institute 25-item Visual Function Questionnaire (NEI VFQ-25), in adults with strabismus.
Design
Prospective case series.
Methods
Fifty-five adult patients in a clinical practice with stable strabismus completed the AS-20 and the NEI VFQ-25 at 2 visits, without intervening treatment. Questionnaires were completed the second time either at a subsequent office visit, immediately before surgery, or by mail. Intraclass correlation coefficients were calculated. Ninety-five percent limits of agreement and 95% confidence intervals around the 95% limits of agreement also were calculated.
Results
There was excellent agreement of overall questionnaire scores for the AS-20 (intraclass correlation coefficient, 0.92) and NEI VFQ-25 (intraclass correlation coefficient, 0.94). The 95% limits of agreement for overall scores were 14.3 points (95% confidence interval, 10.9 to 17.7) for the AS-20 and 11.1 points (95% confidence interval, 8.5 to 13.8) for the NEI VFQ-25. The lower test–retest variability of the VFQ-25 seemed to be partly the result of ceiling effects with many scores at the normal end of the range.
Conclusions
The new AS-20 and the NEI VFQ-25 show excellent test–retest reliability in adults with strabismus. Change exceeding 95% limits of agreement (14 points on the AS-20 and 11 points on the VFQ-25) is indicative of real change in an individual patient. The AS-20 may be more useful than the VFQ-25 because it is less prone to ceiling effects in adults with strabismus.
Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota
Inquiries to Jonathan M. Holmes, Department of Ophthalmology, W7, Mayo Clinic, Rochester, MN 55905
ABSTRACT