Chapter 12 | Experiment with More Than One Independent Variable

What is a factorial design in experiments?

A factorial design is an experiment where two or more independent variables (IVs) are manipulated at the same time. Each combination of levels of the IVs is tested.

What is a 2-way factorial design?

A 2-way factorial design is an experiment with two independent variables (factors), each with two or more levels.

What kinds of information do factorial designs provide?

Factorial designs provide main effects (the effect of each IV separately) and interaction effects (how one IV changes the effect of another IV).

What is a main effect in a factorial design?

A main effect is the overall effect of one independent variable, averaging over the levels of the other variable(s).

What is an interaction in a factorial design?

An interaction occurs when the effect of one IV depends on the level of another IV. In other words, the variables combine in a way that their effects aren’t simply additive.

How do you interpret factorial notation, such as 2 × 2, or 2 × 3 × 4?

Each number represents the number of levels for an IV.

2 x 2: Two IVs, each with 2 levels.

2 x 3 x 4: Three IVs, with 2, 3, and 4 levels respectively.

How many main effects and interactions are possible in a 2 × 2 factorial design?

2 main effects (one for each IV)

1 interaction (how the two IVs combine)

What is a participant variable in a factorial design?

A participant variable is a variable measured in participants (like age or gender) rather than manipulated, but is included in the factorial design alongside manipulated IVs.