Quality of Life (QOL) is an important outcome indicator in health care (Kane, 1997). Many such scales exist. The SF-36 is a quality of life measure; in particular, the 10 item physical functioning item subset (PF-10) has received much interest (Goldfield & Nash, 1999). However, the methodological weaknesses of these types of assessment have also come under question (Groenvold, 1999). A subsample of approximately 3,600 individuals (all individuals with PF-10 scores) was drawn from the Medical Outcomes Study 1986-1992 Radius database (Tarlov et al., 1998). The responses to the PF-10 at baseline, 12, 24, and 48 months were examined using Rasch Rating Scale analysis (Wright & Masters, 1982) to determine the stability of the underlying metric over time. In order for changes in QOL to be an appropriate outcome measure, it is first necessary to demonstrate that the variable defined by the collection of items is invariant across administrations. The Rasch analysis indicates that although the ordering of the items remains relatively constant (r>0.95), there are problems with the fit of items and suggestions that the variable may not be unidimensional. In addition, there is considerable expansion of the range of item difficulty across the 4 assessment dates. The results also indicate some inconsistencies in the Radius database that may not make the results generalizable to other data sets. The methodology used in this analysis can be used as a general guideline to ensure the appropriateness of change scores based on a variety of QOL measures used in Public Health arena.
Learning Objectives: At the conclusion of the session, the participant in this session will be able to: 1. Recognize violations in the analysis of ordinal data that are frequently made in quality of life assessment. 2. Evaluate the stability of the PF-10 over repeated administrations. 3. Assess the methodological issues in change scores for other quality of life scales used in Public Health
Keywords: Quality of Life, Methodology
Presenting author's disclosure statement:
Organization/institution whose products or services will be discussed: None
I do not have any significant financial interest/arrangement or affiliation with any organization/institution whose products or services are being discussed in this session.