Blinded experiment

An experiment in which participants, researchers, or both are kept unaware of treatment assignments to reduce bias in outcomes, observations, or analysis.

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Randomized controlled trial: A study that randomly assigns participants to an intervention or comparison group to estimate causal effects. Blinding often complements random assignment, which balances groups before treatment begins.
Single-blind study: A study in which one group, commonly participants, is unaware of treatment assignments. It is one common arrangement within the broader idea of blinding.
Double-dummy technique: A trial method that gives participants matching placebos for treatments that differ in appearance or administration. It preserves participant masking when two active treatments cannot look alike.
Open-label trial: A trial in which participants and investigators know which treatment is being given. It contrasts directly with masked trials and is used when masking is infeasible or unnecessary.
Placebo: An inactive or sham intervention used as a comparison, often designed to resemble an active treatment. A convincing placebo helps conceal assignment from participants.
Double-blind study: A study in which participants and specified study personnel are unaware of treatment assignments. It masks more than one party, though exact definitions vary across fields.
Sham surgery: A control procedure that mimics surgery without performing its therapeutic component. It can help separate surgical effects from expectations and nonspecific care.
Placebo-controlled trial: A trial that compares an intervention with a placebo rather than, or alongside, another treatment. A placebo comparison can support participant masking, unlike many active-control comparisons.
Allocation concealment: A method that prevents those assigning participants from knowing upcoming treatment allocations. It prevents foreknowledge during enrollment, a distinct safeguard from blinding after assignment.
Triple-blind study: A study design that keeps participants, investigators, and an additional party such as analysts unaware of assignments. It extends masking beyond the participants and treating staff.