Using Rasch and factor analysis to develop a Proxy-Reported health state classification (descriptive) system for Cerebral Palsy

Abstract

Purpose

The Cerebral Palsy quality of life instrument is a well-known health-related quality of life measure for children with Cerebral Palsy. Due to its length it is not suitable as the basis of a preference-based instrument. The aim of this study is to develop a short version of the Cerebral Palsy quality of life instrument that can subsequently be scored as a multi-attribute utility instrument through assigning preference-based values.

Methods

A sample of 473 participants who have a child with Cerebral Palsy completed the Cerebral Palsy quality of life instrument(proxy-version) instrument. After deleting questions related only to the proxy, the dimensional structure was obtained using exploratory factor analysis. Extended Rasch analysis was then undertaken to test the psychometric performance of items and select the best item to represent each dimension. Expert opinion was sought to confirm the dimensions and items.

Results

A six-dimension classification system was identified, in which four domains were extracted from the factor analysis. Following expert opinion, two other domains were also added, as these were considered to have significant impact on health-related quality of life in children with Cerebral Palsy.

Conclusions

The combination of Factor and Rasch analysis along with consultation with patients, clinicians and experts in health-related quality-of-life instrument development, has resulted in a short version of the Cerebral Palsy quality of life instrument.

IMPLICATION FOR REHABILITATION

• This study provides the first classification system for children with Cerebral Palsy.

• The Cerebral Palsy-six dimension (CP-6D) survey, which is a short version of Cerebral Palsy Quality Of Life instrument, can be timesaving when measuring quality of life in children with Cerebral Palsy.

• The short version (CP-6D) can be used in preference based measurement and generate quality adjusted life years for children with Cerebral Palsy.

Keywords:

• Cerebral Palsy
• health related quality of life
• health state classification system
• Rasch analysis
• item response theory

Acknowledgments

The authors would like to thank Kim-Huong Nguyen who provided insight that assisted the developing the research and Shaneen Leishman for her assistance in gathering the data.

Ethical approval

This article does not contain any studies with human participants performed by any of the authors.

Disclosure statement

The Authors declare no conflict of interest.

Additional information

Funding

This study contains data from studies supported by NHMRC project grants including: INCITE study [NHMRC: 368500], Mitti study [NHMRC Career Development Fellowship: 1037220], and Australian CP child study [NHMRC: 465128]. Paul Scuffham is supported by a National Health & Medical Research Council Senior Research Fellowship (NHMRC) [No. 1136923]. Roslyn Boyd is also supported by National Health & Medical Research Council (NHMRC) research fellowship [No. 1105038].