Process Capability, Error in Estimation of

Abstract

Process capability indices (PCIs) are widely used to provide numerical measures of process performance, which have received considerable research attention and increased usage in process assessments and purchasing decisions during the last decade. A substantial majority of capability research works that appeared in the literature do not take into account gauge measurement errors. However, the gauge measurement errors have a significant effect on estimating and assessing process capability since measurement systems are not 100% precise. An inaccurate measurement system can thwart all the benefits of improvement endeavors resulting in poor quality. Analyzing process capability without considering gauge capability may often lead to unreliable decisions. It could result in a serious loss to producers if gauge capability is not being considered in process capability estimation and testing. Since measurement errors unfortunately cannot be avoided, using appropriate confidence coefficients and power becomes an essential task. In this article, we summarize the issue on estimating and testing the process capability is the presence of measurement errors, provide a numerical example discussing the influence of measurement errors, and cite additional references for more discussions on gauge repeatability and reproducibility (GR&R) studies.