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Experimental designs in which every level of every variable is paired with every level of every other variable are called factorial designs. In this example, every level of dosage (0 mg, 100 mg, and 200 mg) is paired with every level of type of task (simple and complex). Also note that this implies that every level of type of task is paired with every level of dosage. This experiment on dosage and type of task is described as a Dosage (3) x Type of task (2) between-subjects factorial design.

Factorial designs can also contain more than two variables. For example, an Age (2) x Dosage (3) x Type of task (2) factorial design would consist of the following 2 x 3 x 2 = 12 conditions.

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