If the capability of a centered process improves, which one of the following might explain the improvement if that is the only change that occurs in the process?

When analyzing the capability of a centered process, the focus is on how well the process output fits within defined specification limits. An improvement in the capability of this process is commonly associated with a decrease in process variation.

When the variation in a process decreases, it means that the produced outputs are more consistently closer to the mean. This makes it more likely that the outputs fall within the upper and lower specification limits, thereby improving the overall capability of the process. With a reduced spread in the data, the process not only yields fewer defects but also produces outcomes that more reliably meet customer requirements, which is a key aspect of process improvement.

In the context of process capability indices (like Cp and Cpk), lower variation leads to higher indices values. Thus, if the process capability improves due to a single modification in the process, it indicates that the process has become less variable, aligning with the correct choice of a decrease in process variation.