From Split to Psycho: why cinema fails dissociative identity disorder

M Night Shyamalan's new movie, Split, stars James McAvoy as a character with 23 different personalities. And, like most screen portrayals of the disorder, it is seen as dangerous and violent. But what's the truth behind the stigma?

Tom Hanks played six different characters in Cloud Atlas, Eddie Murphy played seven in The Nutty Professor and Alec Guinness notched up eight in Kind Hearts and Coronets. But James McAvoy sets a new benchmark with his new movie, Split. He plays Kevin, a man with at least 23 distinct personalities - not all of them nice. This presents extra challenges for the young women Kevin has abducted and locked in his basement. Every time he walks into the cell, they have to work out who they are dealing with. Is it "Dennis", the frowny, buttoned-up neat-freak? Is it "Patricia", the prim, English-accented governess? Could it be "Hedwig", the nine-year-old Kanye West fan? We don't get to see all of Kevin's alter egos, but enough to get the picture and to make this lurid little horror stand out from the crowd.

Split's writer and director, M Night Shyamalan, professes to having had a lifelong fascination with dissociative identity disorder (DID), formerly known as split personality, or multiple personality disorder, and frequently mislabelled as schizophrenia (which is an entirely different condition). He is clearly not the only one. DID is relatively rare in real life, but we have all heard of it, and we all think we know what it entails because cinema and television seem to be obsessed with it.