The researcher manipulates two or more independent variables (factors) simultaneously to observe their effects on the dependent variable, which allows the testing of two or more hypotheses in a single project. This is called

Manipulating two or more independent variables at once to test several hypotheses is a factorial design.

A randomized block design controls one nuisance variable by blocking.

A non-randomized design lacks random assignment of subjects.

Quasi-experimental research works without full random assignment.

A factorial design also reveals interaction effects between the factors.

A two-by-two factorial has two factors at two levels each.