ABSTRACT
A split plot accommodates both hard-to-change (HTC) factors, for example the cavities in a molding process, and those that are easy to change; in this case, the pressure applied to the part being formed. The HTC factor creates so much noise in this process that in a randomized design it would overwhelm the effect of coating. The application of a split plot overcomes the variability by grouping the heats, in essence, filtering out the temperature differences. Split plot designs originated in the field of the agriculture where experimenters applied one treatment to a large area of land, called a whole plot, and other treatments to smaller areas of land within the whole plot, called subplots. George Box in a Quality Quandaries column on the Split Plot Experiments detailed a clever experiment that discovered a highly corrosion-resistant coating for steel bars.
