Dissociative identity disorder (DID), previously known as multiple personality disorder (MPD), is characterized by the presence of at least two personality states or "alters". The diagnosis is extremely controversial, largely due to disagreement over how the disorder develops; two theoretical models lead to opposing conclusions. Proponents of DID support the trauma model, viewing the disorder as an organic response to severe childhood trauma. Critics of the trauma model support the sociogenic (fantasy) model of DID as a societal construct and learned behavior used to express underlying distress, developed through iatrogenesis in therapy, cultural beliefs about the disorder, and exposure to the concept in media or online forums. The disorder was popularized in purportedly true books and films in the 20th century; the 1976 film Sybil became the basis for many elements of the diagnosis, but the film was later found to be a fictionalized account.