Original Article
Performance of the Norwegian SF-36 Health Survey in Patients with Rheumatoid Arthritis. II. A Comparison of the SF-36 with Disease-Specific Measures

https://doi.org/10.1016/S0895-4356(98)00099-7Get rights and content

Abstract

The performance of the SF-36 was compared with disease-specific health status instruments (Arthritis Impact Measurements Scales [AIMS2], Modified Health Assessment Questionnaire [MHAQ] and visual analogue scales) in 1030 patients with rheumatoid arthritis (mean age 62.3 years, 79% females, mean disease duration 12.9 years, 48% rheumatoid factor positive). The scales performed similarly in known group comparisons (age cohorts, disease severity, disease activity, comorbidity). The SF-36 physical functioning scale correlated −0.69 and −0.73 with the MHAQ and AIMS2 physical scales, respectively. A strong negative correlation was found with the walking and bending subscale of AIMS2 (r = −0.80), a substantial negative correlation with mobility (r = −0.65), and moderate correlations with the scales for hand/finger and arm function (r =−0.52 and r = −0.53). Frequency distributions of scores revealed more skewed distributions of the AIMS2 physical scale and the MHAQ scale than the physical functioning scale of the SF36, whereas the pain and mental health scales were distributed similarly. In conclusion, the SF-36 performs well in patients with rheumatoid arthritis. The physical functioning scale of the SF-36 does not seem to capture all aspects of physical health in rheumatoid arthritis patients, but may be more sensitive than disease-specific measures to low levels of physical disability.

Introduction

Assessment of health status in rheumatic diseases has become increasingly important in health service research, epidemiological studies, and clinical trials. Data from such studies may be used to evaluate the benefits of health care and target therapeutic interventions. Disease-specific instruments have been and are still the most widely used for the assessment of patient outcomes in rheumatic diseases. The Health Assessment Questionnaire (HAQ) [1] and the Arthritis Impact Measurement Scales (AIMS) [2] have since 1980 obtained status as standards for measuring disability and health-related quality of life (HRQOL) in rheumatic diseases. The disability part of the HAQ has been modified to a shorter eight-item version (Modified Health Assessment Questionnaire [MHAQ] 3, 4 and the AIMS has been revised, extended, and improved (AIMS2) [5].

Comparisons across different diseases and conditions and with the normal population are more easily obtained with generic than with disease-specific instruments. Such comparisons are important in the context of resource and policy decisions 6, 7. Recently, generic instruments providing health profiles have been used in an increasing number of studies of rheumatic patients. Among these instruments are the Sickness Impact Profile [8] and the Nottingham Health Profile [9].

The SF-36 is a more recently developed generic health status measure providing information for nine different aspects of health status 10, 11, 12. It has been used in a variety of conditions 13, 14 and in musculoskeletal disorders [15], including patients who have undergone knee and hip replacement surgery 16, 17, 18, 19, 20, 21, 22, 23. The SF-36 may be a useful instrument in rheumatoid arthritis (RA) if it’s feasible and if the validity is satisfactory. It may even replace the disease-specific instruments in measuring the general concepts of HRQOL. Few data have been published on its use in RA and other inflammatory arthropathies 24, 25, 26.

The SF-36 has been translated, adapted, and tested cross-culturally among Norwegians according to guidelines from the International Quality of Life Assessment (IQOLA) project 27, 28. This is the second article using the first empirical data set obtained after testing the SF-36 in a large and representative Norwegian patient population with RA [29]. Scores from the SF-36, visual analogue scales (VAS) for pain and fatigue, AIMS2 and MHAQ were obtained from 1030 patients with RA. In this article we compare the performance of the SF-36 with corresponding subscales of the AIMS2 and MHAQ and with scores from VAS measuring pain and fatigue. Correlations between related and unrelated scales are presented and known-group comparisons are used to document the sensitivity of the SF-36 and the other instruments between different cohorts.

Section snippets

Patients

A register of patients with RA has been established in the community of Oslo (472,000 inhabitants) comprising 1552 patients as of January 1994 [30]. The community offers a well organized health service with two rheumatology referral centers (the community department and the University clinic). Specialist referrals are restricted to the community, and there are no full-time private practice rheumatologists. The register includes all patients with RA ever examined at one of the two rheumatology

Results

The left part of Table 1 shows the mean scores of the nine SF-36 scales including reported health transition, the score for the MHAQ, the four main dimensions from the AIMS2 (except role), and the VAS scores for pain and fatigue. The percentage of patients with calculable scores of SF-36 scales ranged from 93.9 to 99.6. Calculable scores were obtained in similar percentages with the AIMS2 (97.6–99.2%) and MHAQ (97.6%), but compliance was lower with VAS (91.7–92.4%). Floor and ceiling effects

Discussion

Our study demonstrates that subscales of the SF-36 generally correlated strongly to VAS and scales from disease-specific measures intended to measure similar concepts. It has been assumed that generic measures are less able than disease-specific measures to discriminate between different levels of disease activity, but this assumption was not supported by the present study. The generic and disease-specific instruments also performed similarly regarding discrimination between patients with and

Acknowledgements

Supported in part with grants from the Norwegian Cancer Association, the Norwegian Research Council, the Norwegian Rheumatism Association, and the International Quality of Life Assessment (IQOLA) Project from Glaxo Wellcome Inc. and Schering-Plough Corporation.

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