What does the process capability ratio (Cp) compare?

The process capability ratio (Cp) is a critical measure in quality control that compares the acceptable tolerances of a process with the actual variability of that process. Specifically, Cp is calculated by taking the difference between the upper and lower specification limits (the acceptable tolerances) and dividing it by six times the standard deviation of the process (which represents the actual process variation). A Cp ratio greater than 1 indicates that the process variation is stable and well within the specified limits, thus demonstrating that the process is capable of producing output that meets specifications consistently.

This relationship is vital in manufacturing and quality assurance as it helps organizations understand whether their processes are capable of producing products that conform to desired specifications. However, the focus on process capability necessitates that acceptable tolerances and actual variation are considered, making this answer the most accurate choice.

In contrast, the other options do not relate to the concept of process capabilities. For example, comparing order quantities with production costs, supplier reliability with delivery times, or production rates with employee performance are metrics related to different aspects of operations management and not specifically tied to process capability measurement.