A wafer fabrication outcome, such as wafer yield or wafer lifetime, is predicted by excluding uncontrollable but measurable internal/external noises of a DOE system, and by rendering relations between wafer design variables and wafer outcome outputs to be more causal, as well as the relations between variances for each of the wafer design variables and the wafer outcome outputs. With the aid of a wafer fabrication outcome predicting model formed by the more causal relations, precision of predicting wafer outcomes can be raised, and performance of wafer fabrication can be thus raised as a result.