Catquest-9SF questionnaire: Validation in a Greek-speaking population using Rasch analysis

PurposeThe Catquest-9SF questionnaire is a tool measuring visual disability and vision-related limitation in patients' daily activities. The primary objective of this study was the validation of Catquest-9SF in a Greek-speaking cataract population.MethodsThe questionnaire was translated into Greek and translated back into English. A pre-final Greek version was formed and tested by 10 Greek-English bilingual participants and by the translation team, and the final version was produced. Patients scheduled for cataract surgery completed the questionnaire preoperatively and postoperatively. Rasch analysis was performed for the assessment of the Catquest-9SF psychometric properties, including response category ordering, item fit statistics, principal components analysis, precision, differential item functioning and targeting for preoperative and postoperative data collectively.ResultsA total of 100 (55 men, 45 women, mean age = 71.94±6.63) cataract patients completed the Greek version of Catquest-9SF questionnaire preoperatively and postoperatively. Rasch analysis showed a significant improvement in the median person Rasch score from -1.49 preoperatively to -4.71 logits postoperatively, while the effect size was 1.3. Unidimensionality was confirmed since infit and outfit mean square values varied between 0.66 and 1.37. Rasch analysis showed good precision and separation ability (Person Separation Index of 3.28, and Person Reliability of 0.92). Four response categories were found for all items. The item-person means difference was -1.83 logits. The difference between preoperative and postoperative Catquest-9SF logit score was positively correlated with preoperative Catquest-9SF logit score (coeff. = 0.798, p