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K. Pesudovs, P. G. Schoneveld, D. J. Coster; The Keratoconus Outcomes Research Questionnaire (KORQ). Invest. Ophthalmol. Vis. Sci. 2007;48(13):1841.
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© ARVO (1962-2015); The Authors (2016-present)
To develop and validate a questionnaire for the measurement of quality of life (QOL) in people with keratoconus: The Keratoconus Outcomes Research Questionnaire (KORQ).
The questionnaire was developed using conventional methods and Rasch analysis to assure content validity, repeatability, construct validity and low respondent burden. Item identification and selection were performed using extensive literature review, professional advice and lay focus groups. Three important content areas were identified: visual disability, symptoms and convenience. Item reduction utilised data obtained from 158 subjects completing a 44-item pilot questionnaire. Response scale performance and the benefit of reduction of the number of response categories was investigated with Rasch analysis.
The final KORQ questionnaire contained subscales for visual disability (14 items) and symptoms (9 items). Both performed optimally with a four-category response scale. These subscales displayed good item to subject targeting, good validity and reliability by Rasch overall model (real person separation reliability 0.92, 0.82 respectively) and item fit statistics. Multidimensionality on principal components analysis precludes combining subscales into an overall score.
Rasch and standard psychometric analyses demonstrated that the 23 item KORQ questionnaire is a valid and reliable measure of QOL in people with keratoconus. A scoring algorithm is provided for KORQ questionnaire users to convert raw scores into the Rasch analysis-derived person measures of visual disability and symptoms.
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