Measurements of process inputs and outputs can be used to optimize the process being measured. Process inputs may be raw materials, human resources or services. All inputs have some quantifiable measurement, including human effort and skill level. Process input requirements should be stated so that key measures of input quality can be controlled. Measurements within the process can also be used as effective controls. Once process capabilities are known, output measures can be used to monitor if the process has remained in control. Feedback from downstream process measurements can be used to improve an upstream process.
For example, electrical testing for solder shorts can be used to optimize a circuit board soldering operation even if it is several processes upstream from the testing operation. When considering the entire organizational feedback system, complex interrelationships are likely to exist. This is where planned experimentation and designing for six sigma comes into play. Planned experimentation deals with isolating the effects of several different, independent variables on a process. Designing for six sigma includes eliminating potential sources of error.
