Variation in the distribution of patient-reported outcomes based on different definitions of defining asthma severity.
OBJECTIVE
The purpose of this study was to observe the variation in the distribution of health-related quality of life and work performance scale scores based on using different methods of determining asthma severity.


METHODS
Five methods of determining asthma severity were used, including three patient-derived measures (patient perceived severity or PPS; overall symptom-derived severity or OSS; and nocturnal symptom-severity or NSS); and 2 methods using retrospective pharmacy claims (reliever/oral steroid use or ROSU and multi-drug use or MDU). Three levels of severity were examined: mild, moderate, and severe, requiring condensing some severity categories of several methods. Data were obtained from a cross-sectional mail survey of 603 adults with asthma in a US managed care organization linked to pharmaceutical/medical claims data. Patient-reported outcomes included the Physical Component Summary Score (PCS) and the Mental Component Summary Score (MCS) of the SF-36, the summary score (AQLQ) of the Asthma Quality of Life Questionnaire, and the Work Performance Scale score (WPS) of the perceived work performance scale of the Functional Status Questionnaire. Analysis of variance (ANOVA) was used to examine each method's ability to distinguish between severity levels. Descriptive statistics were used to observe differences in scale scores between methods.


RESULTS
Within each method, significant severity effects (except MDU) were found for PCS, AQLQ, and WPS. In post-hoc analyses, mild-moderate and mild-severe comparisons were consistently significant (p < 0.05). In the cross-method analyses, method effects were found at all levels of severity for most scale scores with ranges increasing with increases in severity level. Within-method results were consistent with previous studies demonstrating a significant relationship between severity, health-related quality of life (HRQL) and work performance (WP). However, HRQL and WP scale scores varied by the method used to define severity.


CONCLUSIONS
This variation should be considered when performing cross-study comparisons of burden of illness and treatment effects.
Erickson
Steven R
SR
College of Pharmacy, University of Michigan, Ann Arbor, MI 48109-1065, USA. serick@umich.edu
Kirking
Duane M
DM
D000328:Adult; D001249:Asthma / Q000150:complications* / Q000188:drug therapy; D003430:Cross-Sectional Studies; D004651:Employment; D023381:Endpoint Determination; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011788:Quality of Life; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D016896:Treatment Outcome