Premium
Validation, test–retest reliability and norm scores for the Dutch Catquest‐9SF
Author(s) -
Visser Martijn S.,
Dieleman Myrthe,
Klijn Stijn,
Timman Reinier,
Lundström Mats,
Busschbach Jan J. V.,
Reus Nicolaas J.
Publication year - 2017
Publication title -
acta ophthalmologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.534
H-Index - 87
eISSN - 1755-3768
pISSN - 1755-375X
DOI - 10.1111/aos.13287
Subject(s) - cronbach's alpha , rasch model , intraclass correlation , reliability (semiconductor) , medicine , cataract surgery , percentile , population , test (biology) , psychology , clinical psychology , physical therapy , psychometrics , statistics , surgery , mathematics , developmental psychology , paleontology , biology , power (physics) , physics , environmental health , quantum mechanics
Purpose The Catquest‐9 SF questionnaire is a unidimensional, reliable, valid and short patient‐reported outcome measure for quantifying benefits in visual functioning from cataract surgery. Our aim was to develop a formal Dutch translation, calculate norm scores, assess its validity and test–retest reliability and provide an easy way for use in clinical practice. Methods Translation of the questionnaire was performed according to guidelines of the International Society for Pharmacoeconomics and Outcomes Research. Catquest‐9 SF was obtained in 657 patients pre‐ and postcataract surgery. We applied Rasch and classical analyses to determine the questionnaire performance with characteristics such as unidimensionality, reliability, separation and differential item functioning. Test–retest reliability was assessed in another group of 145 patients. A cut‐off value to discriminate between people with and without cataract, norm scores and a reliable change index ( RCI ) were calculated using data from a sample of 916 ‘healthy’ persons from the normal population. Results The Dutch Catquest‐9 SF was unidimensional, and both person and item reliability were high; 0.87 and 0.99, respectively. Cronbach's alpha was 0.94, test–retest reliability was 0.85 and the intraclass correlation coefficient was 0.93. Catquest‐9 SF showed to be responsive to the effect of cataract surgery (effect size = 1.27; p < 0.001). The cut‐off value was −1.90, and RCI was 2.27. A quick‐access table with norm scores and percentiles was established to facilitate clinical interpretation. Conclusion This investigation provides validity and reliability of the Dutch Catquest‐9 SF as well as norm scores and a new tool to facilitate the clinical interpretation of patient scores. This makes Catquest‐9 SF suitable for routine use in clinical practice.