What does a capability index (Cpk) measure?

A capability index, specifically Cpk, measures the ability of a process to produce output within specified limits. It assesses how well a process is performing in relation to its specifications by comparing the process mean to the nearest specification limit, taking into account the variability of the process. A higher Cpk value indicates that a process is more capable of producing products that meet customer requirements, while a lower value suggests that the process may frequently produce outputs that are out of specification.

This measurement is crucial for quality management because it provides insight into the consistency and reliability of a process. Organizations use Cpk to evaluate and improve their processes, ensuring they can consistently meet quality standards and reduce waste. By focusing on producing within these limits, companies aim to enhance customer satisfaction and minimize costs due to defects.