Refinement of the Child Amblyopia Treatment Questionnaire (CAT-QoL) using Rasch analysis
Purpose: The Child Amblyopia Treatment Questionnaire (CAT-QoL) was developed using a “bottom-up” methodological approach. Interviews with children with amblyopia identified items (questions) and response levels to be tested in a draft questionnaire. This study describes the refinement of the descriptive system for the CAT-QoL instrument using the application of Rasch analysis.
Methods: A multi-centre pilot study was conducted, and data collected from 342 participants. Rasch analysis techniques were applied to identify poorly performing items and collapse item response levels.
Results: Disordered response categories were found for each item, requiring adjacent response levels to be combined. Two items were found to have poor fit (cross and happy) and were removed from the measure. No statistically significant differential item functioning (DIF) was found for any item, using person factors of age, sex, or general health. Two items showed some dependency (worried and upset with family), and the poorer fitting item was subsequently removed (upset with family). This resulted in a refined CAT-QoL instrument that consists of 8-items, each with 3-level response scales.
Conclusion: The refined CAT-QoL instrument may be useful in determining how amblyopia treatment affects children, and offers an alternative to generic patient reported outcome measures.