BACKGROUND--Quality of life (QOL) is commonly measured in asthma clinical trials by a questionnaire given before and after treatment. A structured asthma QOL daily diary provides more restricted information but on a daily basis. The validity and use of such a QOL diary was examined in a clinical trial in which two asthma treatments were compared. METHODS--The effects of low dose inhaled steroid (400 micrograms beclomethasone dipropionate, BDP) combined with the long acting beta 2 agonist salmeterol (100 micrograms) (n = 220) was compared with high dose inhaled steroid (1000 micrograms BDP) (n = 206) in asthmatic outpatients in a double blind, parallel group study. Outcome measures consisted of a combined diary for peak expiratory flow (PEF) rate, symptoms, and problems, and an asthma-specific QOL questionnaire, the Living with Asthma Questionnaire. RESULTS--The QOL diary correlated with the QOL questionnaire for both cross sectional and longitudinal assessments. Cross sectional correlations with PEF were higher for the QOL questionnaire than the QOL diary, but longitudinal correlations with PEF were higher for the diary than the questionnaire. Treatment with low dose steroid/salmeterol compared with high dose steroid produced better lung function, better QOL as measured by diary, and reduced night time wakenings, but treatment differences were not obtained with the QOL questionnaire nor for daytime symptoms. Diary assessed QOL was a better predictor of low PEF than diary assessed symptoms. Compliance with diary completion was good but there were floor or ceiling effects in the QOL diary records of about 25% of patients. CONCLUSIONS--Structured QOL diaries are valid instruments that appear to be more responsive to longitudinal change in clinical trials than a QOL questionnaire, but QOL questionnaires provide a more sensitive cross sectional measure of disease severity. Floor and ceiling effects are found in some patients' QOL diaries which limit their usefulness. QOL diary problem events occur during the troughs of a peak flow graph, while symptoms are more widely distributed with respect to peak flow.
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