Dr. Johnson hypothesizes that NutraSweet reduces short-term…

Dr. Johnson hypothesizes that NutraSweet reduces short-term memory. In order to test her hypothesis she gives 10 subjects a beverage containing NutraSweet (treatment group) and 10 subjects a beverage without NutraSweet (control group). She then measures the subject’s ability to recall a list of numbers. What is the independent variable?