Example of Create 2-Level Split-Plot Design

Researchers at a plastics manufacturer want to increase the strength of a plastic. The researchers identify additive percentage, agitation rate, and processing time as the possible factors that affect strength. The temperature at which the plastic bakes also affects strength. To run a completely randomized 4-factor design requires that the researchers bake each combination of the within-batch factor levels individually at one of the two temperature settings. Because the process takes too long, the researchers decide to use a split-plot design. The researchers plan to bake all 8 combinations of additive percent, agitation rate, and processing time at one temperature, and then bake all 8 combinations at the second temperature. They replicate this process so that they use each temperature setting twice. This design results in 32 observations, run in 4 whole plots of 8 subplots each.