Double-blind experiments or tests are used in clinical trials to eliminate the risk of bias both for the study administrator and the patient volunteer. In double-blind experiments, both the volunteers and the trial staff are kept unaware to which control group a volunteer subject is assigned. Assignments may include different dosages of a drug being tested, a placebo, or some other distinguishing factor the study is trying to measure.
In clinical drug trials, the double-blind process involves identical packaging of the drug and placebo and then assigning a unique code name or number to each. The code is known only to the assigning party. The coded packages are then sent to another party that assigns another code name or number. The double coded packages are then sent to the physician for administration to the patient.
In order to be a double-blinded study all members of the research team that interacts with study volunteers must be blinded -- or masked -- to the treatment given.
At the conclusion of the trial, the physician provides records of which package each volunteer received and this information is cross-referenced with the originally assigned codes. The investigator then uses this information along with other result data such as drug response and side effects to determine a drug's usefulness.
Double-blind drug studies are used primarily with human subjects when it is important that they don't know which treatment they are getting. They are kept "blind" to whether they are receiving the active drug or a placebo in order to not be swayed by suggestion.
Double-blind studies are not completely free from bias risk. Sometimes a volunteer in a study might convince them self that they are receiving the active drug and not the placebo even without knowing for certain.
While the advantages of a double-blind trial are clear, there are some disadvantages. The obvious disadvantage to drug sponsors is the extra time and expense of administering a double-blind study. However, in order to be scientifically relevant, drug studies need to follow accepted study protocols that include randomization, double-blinding, and other steps to increase accuracy and maintain safety of drug experiments.
Double-blind statistical tests can more easily be manipulated through fraud. From time-to-time researchers have been exposed for falsifying double-blind trial data and avoid being detected. Sometimes the only way to uncover fabricated trial data is to replicate the study.
Besides scientific misconduct, accidental errors can affect study results. False positives can randomly appear in study data depending on the sensitivity and specificity of the test. Following a practice called "publication bias," some investigators and drug sponsors have published only those studies that show a false positive when previous replication of the study yielded a less than positive result.
The first recorded double-blind experiments were conducted in 1784 by the French Academy of Sciences, according to Richard Holmes' 2009 book, "The Age of Wonder:How the Romantic Generation Discovered the Beauty and Terror of Science."(Pantheon) Researchers with the academy were investigating the ideas of Franz Mesmer who proposed the idea of animal magnetism and “mesmerized” patients.
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In one double-blind study published in the Journal of Alternative Complementary Medicine, researchers tested the effectiveness of a natural botanical compound compared to placebo on patients with alopecia, a common form of hair loss.