Blinding is a way to limit the influence of expectations and other sources of bias during an experiment. This lesson introduces the purpose of blinding, who may be blinded, how common terminology is used, and how the practice developed historically.
Blinding, also called masking, means withholding information that could influence participants or investigators until the experiment is completed. Often the masked information is a participant’s treatment allocation, such as whether they received an active treatment or a placebo.
All flashcards
Blinding
Withholding potentially influential information from specified people in a study to help reduce bias.
Observer-expectancy effect
An investigator’s expectations unintentionally influence participants or study procedures.
Who can be blinded in a study?
Participants, intervention researchers, technicians, outcome assessors, analysts, and other study personnel may be blinded.
Why are labels such as double-blind imprecise?
Their meanings vary and do not specify who was blinded or what information was masked.
Unblinding
Masked information becomes known to someone from whom it was withheld, either through disclosure or inference.
Quiz questions
How did the French Royal Commission on Animal Magnetism use blinding in 1784?Answer: It blindfolded subjects testing claims about objects supposedly filled with vital fluid.
What is one purpose of an active placebo in some drug trials?Answer: It produces side effects in both groups to reduce clues about treatment assignment.
What is post-study unblinding?Answer: Releasing masked information after the study is complete.
How can a blind procedure reduce bias in a police photo lineup?Answer: The officer presenting photographs does not know which person is the suspect.
What effect can poor blinding have on estimated treatment effects?Answer: It can favor the experimental group and inflate the estimated effect.
Based on the Wikipedia article Blinded experiment, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.