Consider the following statements: there are a large number of experimental groups; this design is used when there are inherent differences between subjects and possible differences in experimental conditions; and it is important to bring some homogeneity to each group. Which design is being discussed?

Many groups made homogeneous to handle inherent subject differences describe a randomized block design.

A cross-over design gives each subject successive treatments in sequence.

A factorial design manipulates several factors together.

Any type of block design is too vague for this specific case.

Blocking groups similar subjects before random assignment within blocks.

It reduces variability by controlling a known nuisance variable.