Double-Blind Study
A double-blind study is one where neither the subjects nor the researchers administering the treatment know who is in the treatment group versus the Control Group until data is collected and analyzed.
Why blind both?
- Subjects blinded controls for the Placebo Effect
- Researchers blinded controls for experimenter bias: unconscious cues, differential note-taking, selective reporting
Levels:
- Single-blind: subjects do not know; useful but does not control for experimenter bias
- Double-blind: neither knows; standard for high-stakes clinical trials
- Triple-blind: even the data analysts are blinded
When it can't be done
Some interventions cannot be blinded (surgery, exercise programs, talk therapy). Researchers approximate blinding with sham surgery or “active control” therapies.