In clinical medicine, the randomized, placebo-controlled trial (RCT) is the main accepted method to demonstrate the efficacy of investigational topical skin care drugs, and is generally required in order to obtain U.S. Food and Drug Administration (FDA) approval. A similar but generally less rigorous methodology is adopted in the cosmetic industry for skin care trials.1–3 Volunteers in placebo treatment groups within RCTs often report considerable improvement;4 therefore, interpreting the efficacy results for those given the active is complicated by similar results from those given the placebo.
In relation, psoriasis is a long-lasting, immunologically mediated, often severe inflammatory skin disease affecting approximately 3% of the Caucasian population.5 A class of drugs known as the “biologics” is efficacious in treating psoriasis; however, even well-designed psoriasis RCTs can have significant placebo response rates. When response values are present for both the placebo group and the active group, the additive model predicts efficacy by subtracting the response of the placebo group from the active group.6 However, the observed placebo response may reflect factors not implicit in the general definition of placebo response. These indeterminate factors warrant further investigation to optimize RCT design.