title: Control charts demonstrated limited utility for the monitoring of lung function in asthma.
abstract: 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.
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  Control charts may not be suitable for use in many patients with asthma.
authors.affiliation: Screening and Test Evaluation Program, Sydney School of Public Health, University of Sydney, Edward Ford Building (A27), Camperdown, NSW 2006, Australia. robin.turner@sydney.edu.au
authors.forename: Robin M
authors.initials: RM
authors.lastname: Turner
authors.forename: Andrew
authors.initials: A
authors.lastname: Hayen
authors.forename: Petra
authors.initials: P
authors.lastname: Macaskill
authors.forename: Les
authors.initials: L
authors.lastname: Irwig
authors.forename: Helen K
authors.initials: HK
authors.lastname: Reddel
mesh_terms: D001249:Asthma / Q000188:drug therapy* / Q000503:physiopathology*; D001993:Bronchodilator Agents / Q000627:therapeutic use*; D004359:Drug Therapy, Combination; D005938:Glucocorticoids / Q000627:therapeutic use*; D006801:Humans; D008991:Monitoring, Physiologic; D012129:Respiratory Function Tests; D012985:Software Design
chemical_list: D001993:Bronchodilator Agents; D005938:Glucocorticoids