In the Land of the Blind: Applying a Single-blind Study to Finished Products

By: Johann W. Wiechers, PhD, JW Solutions

Posted: October 13, 2009

Finding something local sometimes requires venturing to the other side of the world. This was my experience with the expression, "In the land of the blind, the one-eyed man in king," which I found also existed in English. According to Brian Budzynski, the Book Editor for Allured Business Media's Allured Books, this expression was recorded by Desiderius Erasmus Roterodamus, a Dutch humanist author who collected more than 3,000 proverbs from the classic literature, including this one, in a book called Adagia. This fact embarrassed me, as Erasmus was one of the greatest philosophers from the Netherlands. Others are Spinoza and Hugo de Groot, which should help correct my image. Although this research took me to the United States, it came close to home, as Erasmus was the unlawful son of a priest that lived in Gouda, the Netherlands, where this author resides. Erasmus was conceived  in Gouda and born close to the Erasmus Bridge in Rotterdam. Clearly, in the land of the blind, the one-eyed man is king. I was completely blind and Kozlowski was the one-eyed queen.

This may have little to do with cosmetic science; however, following the positive feedback from a previous column on the placebo effect, I want to readdress clinical study design in relation to cosmetic claim substantiation—this time discussing when to perform double-blind studies and when to perform single-blind studies.

Double-blind studies are studies in which both the subject participating in the trial and the investigator judging the outcome do not know if the subject received an active formulation or a placebo. Therefore, both the subject and the investigator do not know whether the treatment should have any effect, which removes any form of bias. When one is trying to obtain an objective result on the effectiveness of an active in a formulation, this is the preferred study design in clinical trials.

The essential words in the sentence above are “the effectiveness of an active in a formulation.” This means that most clinical studies performed by suppliers of active ingredients will be double-blind, as they often want to show the effectiveness of an active in a formulation. Assuming the active is active, the supplier will supply the active to a manufacturer of cosmetic products. But the situation changes when the end manufacturer is not interested in showing the effectiveness of the active in its formulation, but will be interested in the effectiveness of the formulation. Therefore, while the supplier in answering whether an active is active, the end manufacturer is trying to answer whether a formulation is active. This differentiation changes the clinical trial design fundamentally. Now a single-blind study is required.

A single-blind study is a study where either the investigator or the subject knows which treatment was received or judged. In most cases, it is the investigator that knows, and this is called a subject blinded trial. In the opposite case, it is the subject that knows, and this is called an investigator blinded trial. Here, some degree of bias would be possible but often only in theory, as will be shown later.