Additional information can be helpful in diagnosis, including the Dissociative Experiences Scale or other questionnaires, performance-based measures, records from doctors or academic records, and information from partners, parents, or friends. A dissociative disorder cannot be ruled out in a single session and it is common for patients diagnosed with a dissociative disorder to not have a previous dissociative disorder diagnosis due to a lack of clinician training. Some diagnostic tests have also been adapted or developed for use with children and adolescents such as the Adolescent Dissociative Experiences Scale, Childrens Version of the Response Evaluation Measure (REM-Y-71), Child Interview for Subjective Dissociative Experiences, Child Dissociative Checklist (CDC), Child Behavior Checklist (CBCL) Dissociation Subscale, and the Trauma Symptom Checklist for Children Dissociation Subscale.Dissociative disorders have been found to be quite prevalent in outpatient populations, as well as within low-income communities. One study found that in a population of poor inner-city outpatients, there was a 29% prevalence of dissociative disorders.There are problems with classification, diagnosis and therapeutic strategies of dissociative and conversion disorders which can be understood by the historic context of hysteria. Even current systems used to diagnose DD such as the DSM-IV and ICD-10 differ in the way the classification is determined. In most cases mental health professionals are still hesitant to diagnose patients with Dissociative Disorder, because before they are considered to be diagnosed with Dissociative Disorder these patients have more than likely been diagnosed with major depressive disorder, anxiety disorder, and most often post-traumatic stress disorder.
These categories are used for forms of pathological dissociation that do not fully meet the criteria of the other specified dissociative disorders; or if the correct category has not been determined; or the disorder is transient.The ICD11 lists dissociative disorders as: 

Dissociative neurological symptom disorder
Dissociative amnesia
Dissociative amnesia with dissociative fugue
Trance disorder
Possession trance disorder
Dissociative identity disorder
Partial dissociative identity disorder
Depersonalization-derealization disorder

Cause and treatment
Dissociative identity disorder
Cause: Dissociative identity disorder is caused by ongoing childhood trauma that occurs before the ages of six to nine. People with dissociative identity disorder usually have close relatives who have also had similar experiences.Treatment: Long-term psychotherapy to improve the patients quality of life. Dissociative amnesia
Cause: A way to cope with trauma. Treatment: Psychotherapy (e.g. talk therapy) counseling or psychosocial therapy which involves talking about your disorder and related issues with a mental health provider. Psychotherapy often involves hypnosis (help you remember and work through the trauma); creative art therapy (using creative process to help a person who cannot express his or her thoughts); cognitive therapy (talk therapy to identify unhealthy and negative beliefs/behaviors); and medications (antidepressants, anti-anxiety medications, or sedatives). These medications help control the symptoms associated with the dissociative disorders, but there are no medications yet that specifically treat dissociative disorders. However, the medication pentothal can sometimes help to restore the memories. The length of an event of dissociative amnesia may be a few minutes or several years. If an episode is associated with a traumatic event, the amnesia may clear up when the person is removed from the traumatic situation.