What is the procedure that experimenters need to use to make sure that participants in both the treatment and control groups are not aware of the purpose of the experiment is known as?

The procedure that ensures participants in both the treatment and control groups are unaware of the experiment's purpose is called "blinding." In a single-blind study, participants do not know whether they belong to the treatment or control group, while in a double-blind study, both participants and experimenters are kept unaware of group assignments. This helps to reduce bias and ensures that the results are more reliable and valid.