What does the process capability index (Cpk) measure?

The process capability index, commonly known as Cpk, is a statistical measure that assesses how well a process is performing in relation to its specifications. Specifically, Cpk indicates how closely a process's output aligns with predetermined specifications with consideration for the process's natural variations. A higher Cpk value signifies that the process is consistently producing output within specification limits, while a lower Cpk suggests that there is a higher probability of producing out-of-specification products.

Cpk is critical because it provides insight into how capable a process is of producing quality products without requiring adjustments or corrections after production. This measurement can help organizations identify areas for improvement and drive efforts toward more consistent quality outcomes.

In contrast, the other choices pertain to different elements of manufacturing and operational performance. Process downtime refers to periods when a machine or process is not in operation, which affects productivity but not directly the process capability related to specifications. Process compliance to human resources involves adherence to employment regulations or policies, which is unrelated to measuring process performance. Overall equipment effectiveness focuses on the efficiency and utilization of equipment, rather than how well the output meets specified dimensions or requirements.

Understanding Cpk is essential for quality management as it aligns production capabilities with customer expectations and regulatory requirements.