A blind or blinded experiment is a scientific experiment where some of the people involved are prevented from knowing certain information that might lead to conscious or subconscious bias on their part, invalidating the results.
For example, when asking consumers to compare the tastes of different brands of a product, the identities of the product should be concealed – otherwise consumers will generally tend to prefer the brand they are familiar with. Similarly, when evaluating the effectiveness of a medical drug, both the patients and the doctors who administer the drug may be kept in the dark about the dosage being applied in each case – to forestall any chance of a placebo effect, observer bias, or conscious deception.
Blinding can be imposed on researchers, technicians, subjects, funders, or any combination of them. The opposite of a blind trial is an open trial. Blind experiments are an important tool of the scientific method, in many fields of research—medicine, psychology and the social sciences, natural sciences such as physics and biology, applied sciences such as market research, and many others. In some disciplines, such as drug testing, blind experiments are considered essential.