Every clinical trial is designed to answer a set of research questions. If you fit the guidelines for a trial, you may be eligible to take part. Each study enrolls patients with certain types of illnesses and certain health status. A study that involves two or more treatments can yield reliable answers only is all the patient cases are the same so they can be compared with each other. Before you and your physician make a decision about your treatment (whether it is in a clinical trial or not), your physician will consider many thing s such as the stage of the illness and your general health. You would most likely be referred to a trial by your doctor or by a doctor who knows your case. Some patients find out about trials from other sources as well, such as advertisements. In any case, you must have a reasonable understanding of your role in a research study and be freely willing to participate.