Final answer:
A double-blind experiment is a scientific testing method where neither the subjects nor the researchers know who is in the control or experimental group, which helps to prevent bias and ensure accurate results.
Step-by-step explanation:
A test or experiment in which information about the test that might lead to bias in the results is concealed from both the tester and the subject until after the test is called a double-blind experiment. This methodology is used to control for both experimenter and participant bias. In such studies, neither the researchers nor the participants know who belongs to the control group or the experimental group.
It's essential in cases where expectations could influence the outcomes, such as the placebo effect, which occurs when a person's belief in the effectiveness of a treatment causes an improvement in their condition. To ensure the validity of the experiment, sometimes deception is required, but it must be followed by a thorough debriefing after the study's conclusion. The placebo group receives a treatment that does not influence the response variable, which helps to measure the effect of the active treatment objectively.