Whole plot and subplot error

The two types of random experimental error present in a split-plot design.

Whole plot error is the variability that occurs between the whole plots in the experiment. Subplot error is the variation from run to run within a whole plot that is not explained by the factors. For example, a large baked goods company uses a split-plot experiment to design a new brownie recipe.

Whole plot 1

Whole plot 2 (replicate of whole plot 1)

Whole plot 3

Whole plot 4 (replicate of whole plot 3)

Whole plot error is the variation between whole plots run at the same temperature. Subplot error is the variation from run to run within a whole plot that is not explained by chocolate and sugar.

Minitab uses whole plot error to calculate the F statistic for the hard-to-change factor. Subplot error is used to calculate the F statistics for all easy-to-change factors and interactions.