Dr. Hershey wants to know if Tylenol or Advil works better to relieve the tooth pain after surgery. He does an experiment with 30 adults. 15 of the adults are given Advil their surgery and 15 are given Tylenol. Each adult is given a 500 mg pill, and the are given each adult immediately after their surgery. One hour after giving the pill, dr. Hershey ask his patients to rate pain. The table below shows the number of patients who felt severe pain, some pain, or little pain while on Advil or tylenol! What are the controlled variables in this experiment? What is the independent variable? What is the dependent variable?