Students were told that they were part of a clinical trial, testing a new topical anesthetic, Trivaricane.They were told that it had proved effective in studies at other universities.In reality, it had NO medical properties.One index finger was rubbed with Trivaricane; the other index finger was left untreated.Next, a mildly painful electrical shock was administered to both fingers.After 1 minute, subjects were asked to rate the pain intensity.The result was an overwhelming decrease in pain for fingers treated with the Trivaricane.This is an example of ______.