Refinement of the Child Amblyopia Treatment Questionnaire (CAT-QoL) using Rasch analysis

ABSTRACT

Aims or 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 consisting of 11 items (sad, feeling on face, hurt, doing schoolwork, cross, how other children treat you, doing things, worried, upset with family, playing with friends, happy). 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. Participants were asked to self-complete the appropriate treatment version of the CAT-QoL questionnaire socio-demographic and clinical data were collected by the clinician using a standardised proforma. A “measure” of child’s health was obtained from the parent by asking how they would rate their child’s health over the previous week. Rasch analysis techniques were applied to refine the questionnaire. Rasch was used to examine response categories and collapse item response levels, identify poorly performing items, and explore local dependency of items.

Results: A total of 331 subjects were included in the study sample, however only 315 were accepted into the RUMM program as a number of subjects had missing questions responses on the CAT-QoL. RUMM also excluded a further 41 subjects as these demonstrated extreme responses. Disordered response categories were found for each item, requiring adjacent response levels to be combined. This was applied to all items, and the model fit was re-examined. Two items were found to have poor fit (cross and happy) and were removed from the measure and the model fit was re-examined. 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 three-level response scales.

Conclusion: The refined CAT-QoL instrument includes the following items: sad, feeling on face, hurt, doing work at school, how other children treat you, doing things, worried and playing with friends. The CAT-QoL can be Rasch scored, with a range of 0–16 where a greater value indicates a worse quality of life (or greater impact of treatment on the individual). The CAT-QoL may be useful in determining how amblyopia treatment affects children, and offers an alternative to generic patient reported outcome measures.

KEYWORDS:

• Amblyopia
• quality of life
• questionnaire
• Rasch analysis

Acknowledgments

Data for this study was collected at the following sites: Bradford Teaching Hospitals NHS Foundation Trust; Doncaster and Bassetlaw NHS Foundation Trust; Harrogate and District NHS Foundation Trust; Maidstone and Tunbridge Wells NHS Trust; Medway NHS Foundation Trust; Sandwell and West Birmingham Hospitals NHS Trust; Sheffield Children’s NHS Foundation Trust; Sheffield Teaching Hospitals NHS Foundation Trust; The Mid Yorkshire Hospitals NHS Trust. The author gratefully acknowledges the support from orthoptists and clinicians at each of the collaborating sites.

This work is produced by the author under the terms of Personal Development Award research training fellowship issued by the NIHR. The views expressed in this publication are those of the author(s) and not necessarily those of the NHS, The National Institute for Health Research or the Department of Health.

Supplementary material

Supplementary material for this article can be accessed here.

Additional information

Funding

This work was supported by the Research Trainees Coordinating Centre [PAS2/RDA/02/012].