d) Factorial design

e) Split plot design

• Used when one of factors is difficult to change or randomize.

• We may use split plot design where we are interested in testing the effect of one factor over a wider variety of condition.
• Requires enough size in main-plots to be split into sub-plots.
• We first look at the effect of main plot treatment, then sub-plot treatment.
• In split plot design, the hard-to-change factors are implemented first, the fields are split in two , then the easier-to-change factors are implemented.

Advantage

• Cheaper to run
• More efficient statistically with increased precision

Disadvantage

• Implementing the design can be difficult and requires advance knowledge of a specific discipline.
• Software packages that assist with the design are hard to find.