A blind can be imposed on any participant of an experiment, including subjects, researchers, technicians, data analysts, and evaluators.
A good clinical protocol ensures that blinding is as effective as possible within ethical and practical constraints.
Unblinding that occurs before the conclusion of a study is a source of experimental error, as the bias that was eliminated by blinding is re-introduced.
In the investigations, the researchers (physically) blindfolded mesmerists and asked them to identify objects that the experimenters had previously filled with "vital fluid".
[citation needed] In 1817, the first blind experiment recorded to have occurred outside of a scientific setting compared the musical quality of a Stradivarius violin to one with a guitar-like design.
[5] In 1865, Claude Bernard published his Introduction to the Study of Experimental Medicine, which advocated for the blinding of researchers.
Unblinding that occurs after the conclusion of a study is not a source of bias, because data collection and analysis are both complete at this time.
In pharmacological trials, premature unblinding can be reduced with the use of an active placebo, which conceals treatment allocation by ensuring the presence of side effects in both groups.
[22] Furthermore, it has been reported that some subjects of clinical trials attempt to determine if they have received an active treatment by gathering information on social media and message boards.
[23] CONSORT standards and good clinical practice guidelines recommend the reporting of all premature unblinding.
[1] Bias due to poor blinding tends to favor the experimental group, resulting in inflated effect size and risk of false positives.
A good clinical protocol ensures that blinding is as effective as possible within ethical and practical constrains.
Studies of blinded pharmacological trials across widely varying domains find evidence of high levels of unblinding.
[28] A 2018 meta-analysis found that assessment of blinding was reported in only 23 out of 408 randomized controlled trials for chronic pain (5.6%).
Additionally, both pharmaceutical sponsorship and the presence of side effects were associated with lower rates of reporting assessment of blinding.
[29] Studies have found evidence of extensive unblinding in antidepressant trials: at least three-quarters of patients were able to correctly guess their treatment assignment.
[32][33][34] Some researchers believe that antidepressants are not effective for the treatment of depression and only outperform placebos due to systematic error.
"[37] A 2018 study on acupuncture which used needles that did not penetrate the skin as a sham treatment found that 68% of patients and 83% of acupuncturists correctly identified their group allocation.
The authors concluded that the blinding had failed, but that more advanced placebos may someday offer the possibility of well-blinded studies in acupuncture.
A prior agreement to publish the data regardless of the results of the analysis may be made to prevent publication bias.
Since the officer is typically aware of who the suspect is, they may (subconsciously or consciously) influence the witness to choose the individual that they believe committed the crime.
There is a growing movement in law enforcement to move to a blind procedure in which the officer who shows the photos to the witness does not know who the suspect is.