Which design approaches testing two or more treatments by using different combinations and evaluating potential interactions?

• A. Multicenter Trials
• B. Factorial Designs
• C. Crossover Design
• D. Parallel Group Design

Answer: (B)

Factorial designs test two or more treatments by combining them in different ways and randomizing participants to those combinations. This approach lets you estimate the main effect of each treatment and also whether the treatments interact—meaning the effect of one treatment depends on the presence of the other. For example, with two treatments at two levels, you’d have four groups: neither treatment, treatment A alone, treatment B alone, and both treatments together. This setup provides information on whether the combined effect is simply additive or if there’s synergy or antagonism between the treatments.

Other designs focus on different aspects: multicenter trials describe where the study runs, not how treatments are combined; crossover designs have the same participants receive multiple treatments in succession, serving as their own control; parallel group designs assign each participant to a single treatment without cross-over to explore separate effects. Factorial designs uniquely enable efficient evaluation of multiple treatments and their potential interactions within one study.