---
title: "Scientific control"
chunk: 4/4
source: "https://en.wikipedia.org/wiki/Scientific_control"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:17:22.864522+00:00"
instance: "kb-cron"
---

Blinding is the practice of withholding information that may bias an experiment. For example, participants may not know who received an active treatment and who received a placebo. If this information were to become available to trial participants, patients could receive a larger placebo effect, researchers could influence the experiment to meet their expectations (the observer effect), and evaluators could be subject to confirmation bias. A blind can be imposed on any participant of an experiment, including subjects, researchers, technicians, data analysts, and evaluators. In some cases, sham surgery may be necessary to achieve blinding.
During the course of an experiment, a participant becomes unblinded if they deduce or otherwise obtain information that has been masked to them. Unblinding that occurs before the conclusion of a study is a source of experimental error, as the bias that was eliminated by blinding is re-introduced. Unblinding is common in blind experiments and must be measured and reported. Meta-research has revealed high levels of unblinding in pharmacological trials. In particular, antidepressant trials are poorly blinded. Reporting guidelines recommend that all studies assess and report unblinding. In practice, very few studies assess unblinding.
Blinding is an important tool of the scientific method, and is used in many fields of research. In some fields, such as medicine, it is considered essential. In clinical research, a trial that is not blinded trial is called an open trial.

== See also ==
False positives and false negatives
Designed experiment
Controlling for a variable
James Lind
Randomized controlled trial
Wait list control group

== References ==

== External links ==
"Control" . Encyclopædia Britannica. Vol. 7 (11th ed.). 1911.