Process Robustness & Noise

A major contribution of D.O.E to "quality engineering" is "process robustness", i.e., the ability to make processes insensitive to the influences of NOISE FACTORS (uncontrollable influences). Noise Factors are incorporated in the experiment at the same time as control factors.

A noise factor is a factor which is either impossible or difficult to control, in physical or economical terms. Examples include ambient temperature, material batch-to-batch variations, change of machine operators and etc. Control factors can sometimes be treated as a noise factor. For example, we may wish to maintain a particular performance of the response variable that holds true within a given range of a control factor.