blinding in anaesthesia (statistics)

Blinding refers to the concealment of group allocation from one or more individuals involved in a clinical research study.The French Academy of Sciences originated the first recorded blind experiments in 1784: the Academy set up a commission to investigate the claims of animal magnetism proposed by Franz Mesmer.


Reason for blinding a study:
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.

Types of Blinding:

1. In a single-blind experiment, the individual subjects do not know whether they are so-called "test" subjects or members of an "experimental control" group. Single-blind experimental design is used where the experimenters either must know the full facts (for example, when comparing sham to real surgery) and so the experimenters cannot themselves be blind, or where the experimenters will not introduce further bias and so the experimenters need not be blind. However, there is a risk that subjects are influenced by interaction with the researchers – known as the experimenter's bias.
2. In double-blind experiments, neither the participants nor the researchers know which participants belong to the control group, nor the test group. They help to lessen the power of preconceived notions or physical cues (e.g., the placebo effect, observer bias, experimenter's bias) to distort the results.The key that identifies the subjects and which group they belonged to is kept by a third party, and is not revealed to the researchers until the study is over.
3. A triple-blind study is an extension of the double-blind design; the committee monitoring response variables is not told the identity of the groups. The committee is simply given data for groups A and B. A triple-blind study has the theoretical advantage of allowing the monitoring committee to evaluate the response variable results more objectively. However, in a trial where the monitoring committee has an ethical responsibility to ensure participant safety and by the time monitoring committees receive data, often the emergency situation has long passed where the monitoring was usually guided by a constellation of trends and their directions.

Uses in Anaesthesia: Double-blinding is relatively easy to achieve in drug studies, by formulating the investigational drug and the control (either a placebo or an established drug) to have identical appearance (color, taste, etc.).

Comments:
Effective blinding can be difficult to achieve where the treatment is notably effective (in cases where the tested drug combinations were so effective that it was deemed unethical to continue withholding the findings from the control group, and the general population), or where the treatment is very distinctive in taste or has unusual side-effects that allow the researcher and/or the subject to guess which group they were assigned to.