In split-plot design, which statement is true about whole plots and subplots?

• A. Whole plots are subdivided into subplots in a split-plot design.
• B. Subplots are larger than whole plots.
• C. There are no replicates in split-plot designs.
• D. Split-plot designs require no replication.

Answer: (A)

Split-plot designs have two levels of experimental units: whole plots and subplots. The main factor is applied to whole plots, and then each whole plot is subdivided into smaller subplots where the subplot factor is applied. This structure—whole plots subdivided into subplots—captures practical constraints in randomization and treatment application, and it creates two sources of experimental error: variation between whole plots and variation within whole plots (subplots). An agricultural example helps: irrigation treatment is assigned to large plots, and inside each plot, different crop varieties are tested in subplots. The statement that whole plots are subdivided into subplots is the accurate description.