blinded study
Meaning of blinded study: A trial designed so that expectation cannot shape the result, by hiding which treatment each person receives.
Definition of blinded study
A blinded study is a trial in which some of those taking part are kept unaware of which treatment each participant receives. Concealing the assignment prevents expectation from coloring how symptoms are reported and how outcomes are judged. In a single-blind design only the participants are unaware; in a double-blind design the researchers are unaware as well.
Why does knowing change the result?
Expectation has measurable effects. Someone who believes a treatment is working reports less pain and better sleep, an effect large enough to rival some drugs. Researchers are pulled the same way: a person who knows a participant received the new treatment may probe harder for improvement, record a borderline finding as normal, or read an ambiguous scan more generously. Neither behavior is dishonest, and neither is fixed by trying harder to be fair. Blinding removes the information rather than the intention.
Who is kept unaware?
| Design | Participant | Researcher or assessor |
|---|---|---|
| Open label | Knows | Knows |
| Single blind | Does not know | Knows |
| Double blind | Does not know | Does not know |
An open label study is sometimes unavoidable, for instance when one arm is an operation and the other a tablet. A single blind study is a compromise. A double blinded design is the stronger of the two, and in many trials the pharmacist, the statistician and the committee judging outcomes are blinded too.
How is blinding maintained in practice?
The comparison treatment is made to look, taste and feel identical: a matching dummy tablet, an identical injection, occasionally a sham procedure. Where two active drugs differ in appearance, each participant may take a real tablet of one and a dummy of the other, an arrangement called double dummy. The code linking each person to a treatment is held separately and can be broken for one individual if an emergency demands it. At the end of a trial, participants and staff are sometimes asked to guess which treatment they were given, which tests whether the blinding actually held.
When does blinding fail?
Distinctive side effects give the game away. A drug that reliably slows the pulse, discolors urine or causes a dry mouth is easy to identify from the inside. Once participants have worked it out, the protection is lost even though the study is still correctly described as blinded. Reporting whether blinding was preserved, and how that was checked, forms part of an honest account of a trial.
Also known as
Used in a sentence
The trial was a double blind study comparing the new tablet against a matching placebo.
Good to know
Blinding removes information rather than intention, and a treatment with distinctive side effects can undo it even in a trial correctly described as blinded.