A blind — or blinded — study is an experiment in which information about the test is masked (kept) from the participant, to reduce or eliminate bias, until after a trial outcome is known.
It is understood that bias may be intentional or unconscious, thus no dishonesty is implied by blinding. If both tester and subject are blinded, the trial is called a double-blind experiment.

Blind testing is used wherever items are to be compared without influences from testers' preferences or expectations, for example, in clinical trials to evaluate the effectiveness of medicinal drugs and procedures without placebo effect, nocebo effect, observer bias, or conscious deception; and comparative testing of commercial products to objectively assess user preferences without being influenced by branding and other properties not being tested.

Blinding can be imposed on researchers, technicians, subjects, and funders. 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 medicinal drug testing, blind experiments are considered essential.

In some cases, while blind experiments would be useful, they are impractical or unethical; an example is in the field of developmental psychology.

Adapted from Wikipedia, the free encyclopedia. Internet. Accessed on June 14, 2016.