The reason a control group is often given an inert treatment relates to the:

1. Simply believing one is being treated can change an outcome. 2. If you are familiar with the phrase placebo effect, you already have some idea as to why this is an important consideration. 3. Giving the control group something inert keeps that belief equal across groups. 4. Any remaining difference can then be attributed to the treatment itself. _Source: OpenStax Psychology 2e (CC BY 4.0), Ch 2 'Psychological Research', sections 2.1-2.4_