Sometimes, researchers will administer a(n) to participants in the control group to control for the effects that participant expectation might have on the experiment.
dependent variable
independent variable
statistical analysis
placebo

placebo

Explanation:

We often hear about placebos being used in pharmacological tests. A placebo is an inert substance, sometimes called a "sugar pill," which can be given in place of the drug being evaluated.

Scientists commonly use placebos to study the effects of a new drug. This is done by providing the drug to a number of people who participate in the trial, while the rest receive another substance that lacks medical or therapeutic properties.  Test participants do not know if they received the placebo or the actual drug. Often, even doctors know which participants ingest the drug and which not until the end of the pharmacological test.

answer; overt behavior;