The paragraph is followed by an incomplete phrase or sentence which summarizes the main idea of the paragraph. Choose the missing words of the phrase or sentence.

Everyone knows that a placebo — a fake medication or sham procedure, typically used as a control in a medical trial — can nonetheless have a positive effect, relieving real symptoms like pain, bloating or a depressed mood. The placebo effect is a result of the patient’s expectation that the treatment will help.
（） of a placebo.