In order to achieve robust design, ideas such as signal-to-noise ratio, two-stage design, error factor, and signal factor have been developed from quality engineering.
In quality engineering, we devise a way to create an Orthogonal Array and incorporate those ideas.
The outer arrangement of Outside Arrangement of Orthogonal Array and Mixed Orthogonal Array are unique to quality engineering.
The outside Arrangement of orthogonal tables is an essential method for assessing variability. In general design of experiments, it is basically unnecessary because it only focuses on the difference in the mean. It is used only when it is necessary to evaluate based on repeated errors.
In addition, when using error factors and signal factors, outer placement is also required.
Mixed Orthogonal Array reflect a design philosophy that prioritizes robust results over statistical rigor.