Relationships among quality of life, severity, and control measures in asthma: an evaluation using factor analysis.
BACKGROUND
Validated psychometric tools measuring quality of life, asthma control, and asthma severity have been developed, but their relationships with each other and with other important patient-centered outcomes have not been rigorously assessed.


OBJECTIVE
To use factor analysis to evaluate the relationships of these validated tools with each other and with other patient-centered outcomes.


METHODS
Surveys were completed by a random sample of 2854 Health Maintenance Organization members age 18 to 56 years with persistent asthma. Surveys included demographic information; validated tools measuring generic (Short Form-12; SF-12) and asthma-specific (Juniper Mini Asthma Quality of Life Questionnaire; AQLQ) quality of life, asthma control (Asthma Therapy Assessment Questionnaire), and asthma symptom severity (Asthma Outcomes Monitoring System); self-described severity, control, and course over time; and history of acute exacerbations.


RESULTS
Principal component analysis suggested a 5-factor model that accounted for approximately 59% of the variability. The most prominent rotated factor reflected asthma symptom frequency (19.4% of variability), was measured by the symptom subscale of the AQLQ, and was the only factor significantly related to the Asthma Therapy Assessment Questionnaire, Asthma Outcomes Monitoring System, or the self-reported assessments of severity, control, or course. Other factors included symptom bother (12.1% of variability), reflected by the environment and emotion AQLQ subscales; activity limitation (13.9% of variability), reflected by the activity AQLQ subscale and the SF-12 physical component scale; mental health (8.3% of variability), reflected by the SF-12 mental component scale; and acute exacerbations (5.0% of variability), not measured by any of the validated scales.


CONCLUSIONS
Distinct components of patient-reported asthma health status can be identified by factor analysis. Distinct constructs of severity versus control cannot be identified by the use of these tools alone.
Schatz
Michael
M
Department of Allergy, Kaiser-Permanente Medical Center, San Diego, CA 92111, USA. michael.x.schatz@kp.org
Mosen
David
D
Apter
Andrea J
AJ
Zeiger
Robert S
RS
Vollmer
William M
WM
Stibolt
Thomas B
TB
Leong
Albin
A
Johnson
Michael S
MS
Mendoza
Guillermo
G
Cook
E Francis
EF
D000293:Adolescent; D000328:Adult; D001249:Asthma / Q000517:prevention & control*; D002140:California; D004644:Emotions; D004781:Environmental Exposure; D005163:Factor Analysis, Statistical; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008875:Middle Aged; D011788:Quality of Life; D012307:Risk Factors; D018434:Sickness Impact Profile; D011795:Surveys and Questionnaires