the cases study design is often used to provide researchers with information concerning rare or unusual phenomena such as multiple personality, a dissociative disorder in which two or more distinct personalities exist within the same individual. Although multiple personality is fairly common in television and popular fiction, it is actually an extremely rare condition. With a disorder this rare, it is essentially impossible to gather a group of individuals to participate in any kind of experimental investigation. As a result, most of what is known about multiple personality and its treatment comes from case studies. One of the most famous cases involved a relatively quiet and humble 25-year-old woman (Eve White) who also exhibited a more playful and mischievous personality (Eve Black), as well as a more mature and confident personality (Jane)(Thigpen & Cleckley,1954,1957). You may recognize this highly publicized case study by the title of the 1957 publication, Three Faces of Eve.