Consistency and validity of patient administered assessment of quality of life by the MOS SF-36; its association with disease activity and damage in patients with systemic lupus erythematosus

Abstract

Objective: To investigate the metric properties and validity of the assessment of quality of life by the MOS Short Form 36 (SF-36) in patients with systemic lupus erythematosus (SLE) and to examine the effect of disease on quality of life.

Methods: Cross sectional study of 150 patients with SLE (age: mean 39.7 yrs, SD 11.4 yrs; 95% female) attending 2 specialist lupus clinics between November 1994 and April 1995. Shortly before or after the consultation patients completed the SF-36 and the MOS SF-20 with an additional question about fatigue (SF-20+) in random order. Disease activity was measured by the British Isles Lupus Activity Group System (BILAG), disease damage by the Systemic Lupus International Collaborating Clinics/American College of Rheumatology (SLICC/ACR) damage index (SLICC).

Results: SF-36 domains were shown to be internally consistent (Cronbach's coefficient alpha > or = 0.71). Significant associations of the SF-36 domains with the corresponding domains of the SF-20+ and with global disease activity measured by BILAG were observed. SF-36 scores in patients with SLE were significantly lower than in controls. Different disease activity levels were significantly associated with different quality of life scores, with excellent ability to record the continuum from good health to serious illness by the SF-36. Disease activity had greater effect on quality of life than age, cumulative damage, or disease duration.

Conclusion: This study shows the SF-36 is internally consistent and proves construct, discriminatory, and criterion validity for the SF-36 and construct validity for the SF-20+ in patients with SLE. The SF-36 is preferred because of its broader scope of questions, its widespread use, and previous international validation for a wide variety of diseases.