The Taguchi method defines two types of factors: control factors and noise factors. An inner
design constructed over the control factors finds optimum settings. An outer
design over the noise factors looks at how the response behaves for a wide range of noise conditions. The experiment is performed on all combinations of the inner and outer design runs. A performance statistic is calculated across the outer runs for each inner run. This becomes the response for a fit across the inner design runs. Table 17.1
lists the recommended performance statistics.