On Capability Indices, Measurement Error, and Guardbanding

ABSTRACT

The capability indices and for a production process are connected to its out‐of‐spec proportion and are tabulated for high‐ and low‐quality processes. When items are measured to determine whether to accept or reject them, the quality of the measurement process is relevant and can be assessed using the consumer's risk (CR) and producer's risk (PR). Conceptually, these represent the acceptance of out‐of‐spec items and rejection of in‐spec items, respectively. These risks are tabulated for different levels of process and measurement quality. Guardbanding is used to reduce the CR by rejecting items with measurements that fall outside the guardbands, which are nested within the specification limits. In this article, we tabulate guardbands relative to a baseline production and measurement process. We consolidate existing results on additive measurement processes from the literature and introduce new findings for a multiplicative measurement process. All results are reproducible with the supplemental R  code.