The Inertial Properties of Quality Control Charts

• Published in: Technometrics Vol. 47; no. 4; pp. 425 - 436
• Main Authors: Woodall, William H, Mahmoud, Mahmoud A
• Format: Journal Article
• Language: English
• Published: Alexandria, VI Taylor & Francis 01.11.2005; Milwaukee, WI The American Society for Quality and The American Statistical Association; American Society for Quality Control; American Statistical Association; American Society for Quality
• Subjects: Applied sciences; Charts; Computer science; control theory; systems; Control charts; Control theory. Systems; Cots; Cumulative sum chart; Exact sciences and technology; Exponentially weighted moving average chart; Inertia; Modelling and identification; Multivariate analysis; Multivariate chart; Quality assurance; Quality control; Sample mean; Shewhart chart; Standard error; Statistical process control; Statistics; Technology; Weighted averages; Statistical process control; Control chart; Shewhart chart; Quality control; Cumulative sum chart; Exponentially weighted moving average chart; Multivariate chart; Exponentially weighted moving average
• ISSN: 0040-1706; 1537-2723
• DOI: 10.1198/004017005000000256

Many types of control charts have an ability to detect process changes that can weaken over time depending on the past data observed. This is often referred to as the "inertia problem." We propose a new measure of inertia, the signal resistance, to be the largest standardized deviation from target not leading to an immediate out-of-control signal. We calculate the signal resistance values for several types of univariate and multivariate charts. Our conclusions support the recommendation that Shewhart limits should be used with exponentially weighted moving average charts, especially when the smoothing parameter is small.