Placebo controlled experiment is a study where controlled group is given a placebo while another group is given the drug that is being tested. This way the results can be compared with the placebo group. Placebo is meant to look just like a treatment or medicine, but in reality is not. It is just a look-alike treatment. All test subjects in a clinical trial must be informed there is a chance they could be in the group receiving the placebo. However, they will not know if they are receiving the placebo. The placebo controlled experiments are intended to avoid biases as well as the expectation mitigation.