Quality of life for post-polio syndrome: a patient derived, Rasch standard scale

Abstract

Objective: To design a disease-specific quality of life (QoL) questionnaire for people with post-polio syndrome (PPS).

Methods: Qualitative interviews were conducted with 45 people with PPS to identify themes and derive potential items reflecting impact upon QoL. After cognitive debriefing, these were made into a questionnaire pack along with comparative questionnaires and posted to 319 patients. The 271 (85%) returned questionnaires were subjected to exploratory factor analysis (EFA) and Rasch analysis.

Results: A 25 item scale, the post-polio quality of life scale (PP-QoL), showed good fit to the Rasch model (conditional chi-square p = 0.156), unidimensionality (% t-tests 2.0: CI 0.7–3.8), and Cronbach’s alpha of 0.87. With the latent estimate transformed to a 0–100 scale, the mean score was 56.9 (SD 18.5) with only 3.3% of respondents at the floor or ceiling of the scale. Test–retest reliability showed an intraclass correlation coefficient (ICC) (2.1) of 0.916, and correlation of 0.85.

Conclusion: The disease-specific PP-QoL demonstrated excellent reliability, appropriate concurrent validity, and satisfied the standards of the Rasch model. It enables examination of the impact of health status upon perceived QoL, and the impact of rehabilitation interventions. The scale is freely available for academic or not-for-profit users to improve research in this neglected, disabling condition.

Implications for Rehabilitation

• In post-polio syndrome (PPS), existing work examines aspects of health-related quality of life (HRQoL), such as activity limitations.

• A disease-specific QoL measure would enable researchers to model the impact of health status, such as fatigue or mobility restrictions, upon QoL in PPS.

• The post-polio quality of life scale (PP-QoL) is based on the patients’ lived experience, meets Rasch standards and is free for use for academic and not-for-profit researchers.

• The raw score is reliable for individual use in clinical settings, and interval scale transformation is available for parametric applications and the calculation of change scores.

Keywords:

• Post-polio quality of life scale
• post-polio syndrome
• Rasch analysis
• patient reported outcome measure
• trajectories of outcomes in neurological conditions
• quality of life

Acknowledgements

We would like to give special thanks to our participants, who graciously gave their time to take part in this study. We would like to thank Shruti Kaushal, Frances Quinn and Charlotte Taylor for their contributions to the overall study.

Disclosure statement

The authors report no conflicts of interest.

Additional information

Funding

This work was supported by grant PPS-1 from the Neurological Disability Fund of the Walton Centre NHS Foundation Trust.