Control charts demonstrated limited utility for the monitoring of lung function in asthma.

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Journal Article
Journal of clinical epidemiology, 2012, 65 (1), pp. 53 - 61
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OBJECTIVE: Statistical process control charts have been advocated for use in monitoring of lung function in asthma. We aimed to evaluate their application in asthma using existing data from a randomized trial. STUDY DESIGN AND SETTING: Patients on optimal inhaled corticosteroid/bronchodilator therapy (n=81) were randomized to continue the same or change to corticosteroid alone. Baseline statistical control was assessed from 20 days of electronically recorded lung function (peak expiratory flow [PEF], forced expiratory volume in one second [FEV(1)]). The ability to detect lung function changes was assessed during 10 days after randomization. RESULTS: PEF measurements were in statistical control during baseline for only 59-79% of patients for different combinations of five control chart rules (e.g., Rule 1: >3 standard deviations outside mean and 95% expected to be in control), with similar proportions for FEV(1). After randomization, among those previously in statistical control, Rule 1 signaled lower FEV(1) for 35% of patients randomized to treatment change compared with 6% continuing baseline treatment (P=0.004). Control charts performed poorly for PEF, signaling a decrease for 8% of patients randomized to treatment change compared with 11% continuing treatment (P=0.7). A paradoxical increase was signaled for many patients continuing treatment. CONCLUSION: Control charts may not be suitable for use in many patients with asthma.
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