The validity of generic and condition-specific preference-based instruments: the ability to discriminate asthma control status.
OBJECTIVE
A goal of asthma management is to improve the patient's health-related quality of life (HRQL). However, it is unclear whether HRQL instruments can discriminate across asthma control measures. The objective of this study was to evaluate the validity of generic and condition-specific preference-based instruments, in terms of their ability to distinguish asthma control.


METHODS
Asthma patients (n = 157) completed three generic preference-based instruments: the Health Utility Index Mark 3 (HUI-3), the EuroQol (EQ-5D), and the Short Form 6D (SF-6D) and two condition-specific questionnaires: the standardized Asthma Quality of Life Questionnaire (AQLQ(S)) and the Asthma Control Questionnaire (ACQ). The AQLQ(S) scores were converted into the condition-specific preference-based scores: the Asthma Quality of Life Utility Index (AQL-5D).


RESULTS
The preference-based instruments were generally able to discriminate across control measures, such as ACQ scores and magnitude of asthma medication, but were not able to discriminate for self-reported control and severity levels. These instruments also correlated with most control measures (r = 0.32-0.37). Significant relationships between AQL-5D scores and all control variables were observed.


CONCLUSIONS
Overall, the AQL-5D discriminated across all levels of asthma control. The HUI-3, the EQ-5D, and the SF-6D differentiated between the highest and lowest levels of control but could not discriminate between the moderate levels.
McTaggart-Cowan
Helen M
HM
Centre for Clinical Epidemiology and Evaluation, Vancouver Coastal Health Research Institute, 7th Floor, 828 West 10th Avenue, Vancouver, BC, Canada, V5Z 1L8.
Marra
Carlo A
CA
Yang
Yaling
Y
Brazier
John E
JE
Kopec
Jacek A
JA
FitzGerald
J Mark
JM
Anis
Aslam H
AH
Lynd
Larry D
LD
D000328:Adult; D001249:Asthma / Q000517:prevention & control* / Q000523:psychology; D001955:British Columbia; D005260:Female; D006304:Health Status; D006305:Health Status Indicators; D006306:Health Surveys; D006801:Humans; D008297:Male; D011594:Psychometrics; D011788:Quality of Life / Q000523:psychology*; D012129:Respiratory Function Tests; D011795:Surveys and Questionnaires