In a study about pain relievers, doctors wanted to know if different pain relievers are more effective at relieving pain after surgery than others. Doctors gave subjects Tylenol, Advil, Aleve and aspirin. Each type of pain reliever was given at the maximum recommended dosage. Doctors then asked the subjects about their pain levels over a six hour period. What would be the dependent variable in this experiment? the pain levels experienced by the subjects the age of the subjects the dosage of the pain reliever the types of pain reliever