PURPOSE: To assess and optimize the Catquest questionnaire for measuring patient-reported outcomes of cataract surgery using Rasch analysis.

METHOD: Catquest questionnaires (n = 21364) from the Swedish National Cataract Register were selected and randomized to 2 groups. Data from 10486 questionnaires were comprehensively Rasch analyzed using a 4-Andrich rating scale model in Winsteps software. A revised version of Catquest was developed (Catquest-9SF) and tested in 10886 patients for validity and responsiveness to cataract surgery.

RESULTS: Only the visual disability subscale formed a valid measurement scale. This could be enhanced through the addition of the 2 global assessment items; however, the symptoms and frequency of performing the activities items did not contribute to the measurement. The 9-item short- form version (Catquest-9SF) had ordered response thresholds and good person separation (2.65) and was largely free from differential item functioning. All items fit a single overall construct (infit range, 0.75 to 1.29; outfit range, 0.70 to 1.39) and unidimensional by principal components analysis. The items were well targeted to the preoperative participants (0.34 logit difference in means). The score correlated with visual acuity (r = 0.43 preoperatively; r = 0.48 postoperatively) and was highly responsive to cataract surgery (preoperatively –0.32 ± 2.15 logits; postoperatively –3.21 ± 2.50 logits (P<.0001).

CONCLUSIONS: The 9-item Rasch-scaled Catquest-9SF was highly valid in measuring visual disability outcomes of cataract surgery. Its brevity makes it suited to routine clinical use, and a raw-data to Rasch-measure conversion simplifies application.

    Catquest-9SF   as PDF (420 Kb)

Catquest-9SF Toolkit The Catquest-9SF questionnaire and a Raw score to Rasch score conversion sheet are freely available to researchers for use in their own setting, and both can be downloaded here. Catquest-9SF questionnaire   (25 Kb) Raw score to Rasch score conversion sheet  (208 Kb)

Index of Papers