There are two reasons why. First, the treatment is still experimental. The researchers won't know how well it works until they finish the study and see how people respond. Second, not everyone gets the treatment. The control group gets a pill or shot that has no medicine.
Researchers compare the control group to the treatment group.
For example, if you heard that 60 percent of a treatment group got better, you might be impressed unless you knew that 60 percent of the control group also got better without the medicine. Before you sign up, ask about the study. Usually, you must meet certain guidelines to be in a study. For example , if you have type 1 diabetes, a study on type 2 diabetes would not want you. If you do not have nerve disease, you couldn't join a study on treatments for nerve disease.