A placebo is best described as a treatment that is:

1. A placebo has to be indistinguishable from the real treatment to the subject. 2. The control group is given a placebo treatment. 3. That is an active treatment that cannot directly influence the response variable. 4. If it were obviously fake, subjects would know which group they were in. 5. It is given to the subjects in the control group, not to the researchers. _Source: OpenStax Introductory Statistics 2e (CC BY 4.0), Ch 1 'Sampling and Data', sections 1.1-1.4_