Placebo effect and masking
The placebo effect is a phenomenon in which a patient's symptoms can improve after receiving a treatment that has no active therapeutic effect, such as a sugar pill. This can happen because patients expect the treatment to work and their belief in the treatment can influence their symptoms.
Masking or blinding is a strategy used in research to limit the effects of knowing whether or not a subject is getting therapy. The use of a placebo is one way to mask a subject from knowing whether they are receiving an active treatment or agent or whether they are in the control group. The strategy of double blinding � is to mask observers and data collectors from knowing which group the subjects are in.