Construct and criterion validity of the short form-6D utility measure in patients with systemic lupus erythematosus.
OBJECTIVE
Preference-based measures, such as the Short Form-6D (SF-6D), allow quality-adjusted life-years, used in cost-utility evaluations, to be calculated. We investigated the construct and criterion validity of the SF-6D in patients with systemic lupus erythematosus (SLE).


METHODS
Female patients with SLE were recruited from outpatient clinics at 2 timepoints, 5 years apart. Cross-sectional correlation of the SF-6D with domains of the disease-specific LupusQol health-related quality of life (HRQOL) measure, the Systemic Lupus International Collaborating Clinics Damage Index (SDI; for damage) and Systemic Lupus Erythematosus Disease Activity Index (SLEDAI; for activity) measures, and patient characteristics was tested. The ability to discriminate between groups defined by smoking status, presence/absence of carotid plaque, depression, and fatigue was tested using the t-test.


RESULTS
In total 181 patients were recruited at baseline. The SF-6D correlated moderately to strongly with all domains of the LupusQoL (0.6-0.8) apart from intimate relationships (0.42) and body image (0.34). Correlations of the SF-6D with the demographic and disease-specific measures at baseline were small for the SDI score (-0.23) and age (-0.19) and in the expected direction. The SF-6D did not correlate with disease activity (SLEDAI -0.08). The SF-6D could distinguish those who smoked, had carotid plaque, had depression, and reported fatigue from those who did not, with the largest effect size being for depression (0.75).


CONCLUSIONS
The SF-6D displays construct and criterion validity for use in patients with SLE, but the low correlation with aspects of intimate relationships and body image represents a concern and reinforces the need to collect disease-specific measures of HRQOL alongside generic preference-based instruments.
Address correspondence to Prof. I. Bruce, Arthritis Research UK Epidemiology Unit, The University of Manchester, Manchester Academic Health Sciences Centre, Oxford Road, Manchester, M13 9PT, UK.
Mark J
MJ
Harrison
Yasmeen
Y
Ahmad
Sahena
S
Haque
Nicola
N
Dale
Lee-Suan
LS
Teh
Neil
N
Snowden
Pauline
P
Ho
Rachel
R
Gorodkin
Ian N
IN
Bruce
D000328:Adult; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D006306:Health Surveys / Q000379:methods* / Q000592:standards*; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000175:diagnosis* / Q000453:epidemiology* / Q000523:psychology; D008875:Middle Aged; D011795:Surveys and Questionnaires / Q000592:standards*