<P> A blind or blinded - experiment 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 . </P> <P> 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, 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 . </P>

When is an experiment considered to be double-blind