18 The use of Factor and Rasch analysis to aid decisions for items inclusion in a disease-specific quality of life questionnaire for venous leg ulcers (202)

Simon Palfreyman, Research Nurse, Northern General Hospital, Sheffield Teaching Hospitals NHS Trust, Sheffield, United Kingdom
Co authors: John Brazier & Jonathan Michaels

Abstract:

Background:

The current disease-specific quality of life questionnaires used to examine quality of life (QoL) in people with venous leg ulcers have limitations in both design and validation (Walters 1999).

Aims:

To use a bottom up approach to develop a QoL instrument that could be used to assess the outcome of treatments.

Methods:

Items for inclusion in a questionnaire were generated using qualitative techniques including semi-structured interviews (n = 31) and focus groups. Levels were assigned to the items and the questionnaire piloted to assess face and construct validity. A self-completed postal questionnaire containing sixteen disease specific items was sent to 266 people with a history of venous ulceration. A Rash and factor analysis was carried out to assess the measurement properties and factor structure of the questionnaire.

Results & discussion:

A response rate of 57% (n=152) was obtained. 92 respondents had a current ulcer, the remaining 60 had a healed ulcer. Cronbach’s alpha for the questionnaire was 0.93. Prinicipal component analysis revealed the presence of three components but parallel analysis demonstrated that only two should be retained. Due to correlation between the components (r = 0.5) analysis using the Promax oblique rotation method was used. A two factor structure described direct and indirect effects of venous ulceration. Rasch analysis that assessed the ordering of thresholds, differential item functioning and item fit, resulted in a unidimensional 11-item questionnaire: as five items were shown to be misfitting.

Conclusion:

Factor and Rasch analysis were able aid the identification of items to be included in a quality of life questionnaire. It remains necessary to fully explore the psychometric properties of the instrument including, responsiveness to change in QoL associated with treatment. We propose to describe the process, results and challenges encountered and also examine the potential applicability to other areas of nursing.

Biography:

Simon currently works as a research nurse at the Sheffield Vascular Institute at the Sheffield Teaching Hospitals NHS Foundation Trust. He was awarded the Smith and Nephew Foundation Doctoral Studentship in 2005 to examine quality of life and venous leg ulcers. He has a honorary lecturers post in the Department of Acute and Critical Care, University of Sheffield School of Nursing.