Analyzing a Plackett-Burman Design

Plackett-Burman designs are an alternative to fractional-factorial screening designs. Two-level fractional factorial designs must, by their nature, have a number of runs that are a power of two. Plackett-Burman designs exist for 12-, 24-, and 28-run designs.

The Weld-Repaired Castings.jmp sample data table uses a Plackett-Burman design, and is found in textbooks such as Giesbrecht and Gumpertz (2004) and Box, Hunter, and Hunter (1978). Seven factors are thought to be influential on weld quality. The seven factors include Initial Structure, Bead Size, Pressure Treatment, Heat Treatment, Cooling Rate, Polish, and Final Treatment. A Plackett-Burman design with 12 runs is used to investigate the importance of the seven factors. The response is

. (There are also four terms that were used to model error that are not used in this analysis.)

Using the Fit Two Level Screening platform, select the seven effects as X and Log Life as Y. (If terms are automatically populated in the Fit Two Level Screening platform launch window, remove the four error terms listed as effects.) Click OK. Screening Report for Weld-Repaired Castings.jmp appears, showing only a single significant effect.

Screening Report for Weld-Repaired Castings.jmp

Note asterisks mark four terms, indicating that they are not orthogonal to effects preceding them, and the obtained contrast value was after orthogonalization. So, they would not match corresponding regression estimates.