1.4.4 - Control and Placebo Groups

control group is an experimental condition that does not receive the actual treatment and may serve as a baseline. A control group may receive a placebo or they may receive no treatment at all. A placebo is something that appears to the participants to be an active treatment, but does not actually contain the active treatment. For example, a placebo pill is a sugar pill that participants may take not knowing that it does not contain any active medicine. This can lead to a psychological phenomena called the placebo effect which occurs when participants who are given a placebo treatment experience a change even though they are not receiving any active treatment. Researchers use placebos in the control group to determine if any differences between groups are due to the active medicine or the participants' perceptions (the placebo effect).

Control Group
A level of the explanatory variable that does not receive an active treatment; they may receive no treatment or a placebo
Placebo Group
A group that receives what, to them, appears to be a treatment, but actually is neutral and does not contain any active treatment (e.g., a sugar pill in a medication study)

Example: Vitamin B Energy Study Section

Researchers want to know if adult women who consume a drink that is high in vitamin B-12 have increased energy. They obtain a representative sample of adult women. All of the women are given a drink that they are told to consume every morning. They are not told what is in the drink. Half of the women are given a drink that is high in vitamin B-12 while the other half are given a drink that tastes the same but contains no vitamin B-12.

The women who received the drink with no vitamin B-12 are the placebo group. The purpose of the placebo group in this study is to make the two groups equivalent except for the presence of the vitamin B-12. By comparing these two groups, the researchers will be able to determine what impact the vitamin B-12 had on the response variable. We could also say that this served as a control group because this group did not receive any active ingredients.