Using Control Chart Method to Monitor Occupational Asthma

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Fazel Hayati
PhD, Edgewood College

Saeed Maghsoodloo
PhD, Auburn University

Peter Boggs
MD, The Asthma-Allergy Clinic and Research Center

Occupational asthma is the most prevalent respiratory disorder in the industrial world. This research offers quality control chart methods as an effective tool to detect and monitor workers at risk for occupational asthma. We provide guidelines for practitioners to facilitate early intervention.

The purpose of this research was to investigate whether the Shewhart control chart method can be used as an effective method to detect and monitor occupational asthma. Peak expiratory flow (PEF), a lung function marker, from 45 workers was used for this study. Control charts of PEF measurements at work and away from work were constructed. Multiple rules were developed and investigated. Reviewing the results, the best rule showed a sensitivity of 85.71%, specificity of 87.50%, and an error rate of 13.33% in detecting occupational asthma. Excluding the dubious cases, the test produced a sensitivity of 95.24%, a specificity of 95.83% and an error rate of 4.44%. Also, the Average and Range control chart provided a method to monitor the acute and chronic conditions of asthma and characterize the PEF variability. The magnitude of variation was estimated using Variability Index. Further, the control chart method detected the increase in diurnal variation no matter which index of diurnal variation was used. Our results were as good as and in some cases better than published clinical guidelines. Our research showed that the control chart method is an effective, simple and inexpensive tool for early intervention in workers suspected for occupational asthma.