The metrics of a Six Sigma project reflect customer needs and ensure that the internal metrics of the organization are achieved. The selection of project metrics is one of the crucial elements in the Define phase of the Six Sigma methodology.
A primary metric, also called a project CTQ, is a CTQ measure that is used to monitor project progression and success. It is the reference point throughout the Six Sigma project. Ideally, project CTQs should have direct impact on customers. For any Six Sigma project, the primary metrics should be:
A secondary metric, also known as a consequential metric, is a project metric that you do not want to sacrifice at the expense of primary improvements in a process. These metrics ensure that the process is improving and not shifting one metric at the expense of another. It means that the secondary metrics have a relationship with the primary metrics of a Six Sigma project. Therefore, the primary goal of a Six Sigma project will be to move the primary metrics, but ensure that secondary metrics do not deteriorate or stay constant. Some of the secondary metrics include cycle time, volume shipped, inspection data, and rework hours. These metrics should not be sacrificed to achieve the primary metrics such as customer satisfaction, on-time delivery of products, and final product quality.