**A two-by-two factorial design refers to the structure of an experiment that studies the effects of a pair of two-level independent variables.** The independent variables are manipulated to create four different sets of conditions, and the researcher measures the effects of the independent variables on the dependent variable.

If an experiment involves one three-level independent variable and one two-level independent variable, it is a three-by-two factorial design with six different sets of conditions for study. Although most experiments involve only one independent variable, according to CSU Fresno, factorial design experiments provide the opportunity to study the effects of variables more efficiently while more realistically replicating real-world conditions.