Dissociative identity disorder
There have been no large-scale studies to learn how common DID is. The ISSTD says DID occurs in between 1 and 3% in the general population, and between 1 and 5% in groups of patients in hospitals.  DID is more common in women than in men but this may be caused by men with DID being sent to prison instead of hospitals.  The number of people diagnosed with DID increased from about 200 in 1970 to about 20,000 in the 1990s.  According to the ISSTD this is because doctors did not have the training or experience to recognize DID.  Instead they diagnosed people with depression, PTSD or borderline personality disorder.  People who support the SCM say the increase in diagnoses was because a small number of doctors diagnosed a large number of people and because a large number of therapists began using types of psychotherapy that made people think they had DID.