For instance, "double-blind" could mean that the data analysts and patients were blinded or the patients and outcome assessors were blinded or the patients and people offering the intervention were blinded, etc. ĬONSORT guidelines state that these terms should no longer be used because they are ambiguous. However, the meaning of these terms can vary from study to study. Most often, single-blind studies blind patients to their treatment allocation, double-blind studies blind both patients and researchers to treatment allocations, and triple-blinded studies blind patients, researcher, and some other third party (such as a monitoring committee) to treatment allocations. These terms describe experiments in which (respectively) one, two, or three parties are blinded to some information. In medical research, the terms single-blind, double-blind and triple-blind are commonly used to describe blinding. These biases are typically the result of subconscious influences, and are present even when study participants believe they are not influenced by them. Unblinded data analysts may favor an analysis that supports their existing beliefs ( confirmation bias). Likewise, failure to blind researchers results in observer bias. Patient-reported outcomes can be different if the patient is not blinded to their treatment. Background Bias Ī number of biases are present when a study is insufficiently blinded. The need to blind researchers became widely recognized in the mid-20th century. Webber to investigate the effects of caffeine. The first study recorded to have a blinded researcher was conducted in 1907 by W. This suggestion contrasted starkly with the prevalent Enlightenment-era attitude that scientific observation can only be objectively valid when undertaken by a well-educated, informed scientist. Bernard recommended that the observer of an experiment should not have knowledge of the hypothesis being tested. One early essay advocating the blinding of researchers came from Claude Bernard in the latter half of the 19th century. This trial contested the effectiveness of homeopathic dilution. Īn early example of a double-blind protocol was the Nuremberg salt test of 1835 performed by Friedrich Wilhelm von Hoven, Nuremberg's highest-ranking public health official, as well as a close friend of Friedrich Schiller. A violinist played each instrument while a committee of scientists and musicians listened from another room so as to avoid prejudice. 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. In the investigations, the researchers (physically) blindfolded mesmerists and asked them to identify objects that the experimenters had previously filled with "vital fluid". The first blind experiment was conducted by the French Royal Commission on Animal Magnetism in 1784 to investigate the claims of mesmerism as proposed by Charles d'Eslon, a former associate of Franz Mesmer. In clinical research, a trial that is not a blinded trial is called an open trial. In some fields, such as medicine, it is considered essential. īlinding is an important tool of the scientific method, and is used in many fields of research. The CONSORT reporting guidelines recommend that all studies assess and report unblinding. 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 particular, trials on pain medication and antidepressants are poorly blinded. Unblinding is common in blinded experiments, particularly in pharmacological trials. For example, a patient who experiences a side effect may correctly guess their treatment, becoming unblinded. A good clinical protocol ensures that blinding is as effective as possible within ethical and practical constraints.ĭuring the course of an experiment, a participant becomes unblinded if they deduce or otherwise obtain information that has been masked to them. For example, it is not possible to blind a patient to their treatment in a physical therapy intervention. In some cases, while blinding would be useful, it is impossible or unethical. A blind can be imposed on any participant of an experiment, including subjects, researchers, technicians, data analysts, and evaluators. Good blinding can reduce or eliminate experimental biases that arise from a participants' expectations, observer's effect on the participants, observer bias, confirmation bias, and other sources. In a blind or blinded experiment, information which may influence the participants of the experiment is withheld until after the experiment is complete. Experiment in which information about the test is masked to reduce bias
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