Quality control chart method for analyzing PEF variability in occupational asthma.

BACKGROUND: Asthma is the most common occupational respiratory disorder in the industrialized world. In this research we investigated the effectiveness of quality control chart as a method to explore the work-relatedness of asthma using peak expiratory flow (PEF) as the variable of interest. METHOD: PEF measurements were recorded from several workers suspected of having occupational asthma. The measurements were recorded for a period of 2 weeks at work and two away from work. For each subject, average [symbol: see text] quality control chart was developed and analyzed using Shewhart methods. RESULTS: Using the ratio of average daily PEF diurnal variation at work to the baseline average diurnal variation, quality control chart detected and characterized increased variation in PEF between the periods at workplace and away from workplace. This ratio was evaluated at 15% and 20% and compared to the results of the gold standard. A ratio of greater than 15% produced a sensitivity of 94% and specificity of 61%. These results are as good as and in some cases better than the previously published work. CONCLUSIONS: Quality control chart is an effective and inexpensive method for early intervention to detect workers suspected for occupational asthma. Also, the findings in this article are an invitation for further research in occupational asthma using quality control chart methods for other indices of airways obstruction (FEV-1, RAW) or inflammation (NO).

Control chart for monitoring occupational asthma.

INTRODUCTION: Work-related asthma has become the most prevalent occupational respiratory disease in the developed world. Occupational asthma is thought to affect 5%-10% of people worldwide. The first step in the diagnosis of occupational asthma is to establish work-relatedness. Although considerable research has been conducted in the area of occupational asthma, no simple, effective, and statistically sound method has been developed that can be used as an initial step to effectively identify the workers at risk for occupational asthma. The purpose of this research was to investigate whether Shewhart control chart method can be used as an effective method to detect occupational asthma. METHOD: Forty-five workers who completed the study and provided usable peak expiratory flow (a lung function marker) recordings while at work and away from work were included in this study. Control charts were developed using Shewhart's Method. The lower control limit of at work control chart (LCL(W)) was compared to each subject's Personal Best (PB) value. RESULTS: Reviewing the results of this comparison showed LCL(W)<60% PB to have a sensitivity of 85.71%, specificity of 87.50%, and an error rate of 13.33%. When the subjects suspected for false positive and false negative diagnoses were identified, the test produced a sensitivity of 95.24%, a specificity of 95.83% and an error rate of 4.44%. CONCLUSIONS: Our results were as good as, and in some cases better than, published clinical guidelines. IMPACT ON INDUSTRY: Our research showed that the control chart method is an effective, simple, and inexpensive tool for early intervention in workers suspected for occupational asthma.