Phase III trials compare the results of participants taking the new treatment with the results of participants receiving the standard treatment. Phase III studies typically compare which group lives longer and have fewer side-effects. Participants are randomly assigned to the new treatment or to the standard treatment. Researchers assign the participants by chance to one of the treatment groups. This process is called randomization and it helps make sure that accurate and true results are obtained.
When participants know what group they were randomized to it may change the way they react or feel, so it is important that the participant not know what group they were randomized to. This is called a blinded study. In a double blind study neither the participant nor the physician knows which treatment the participant is receiving. This helps prevent any personal bias from influencing the study results.