With contestants lined up on the lawn of a grand house and looking as if they mean business, the opening sequence of Horizon: How Mad Are You? could be mistaken for The Apprentice. But the 10 "contestants" in the BBC2 programme aren't competing for prizes. They are willingly being scrutinised by psychiatric professionals who have to spot which five have a diagnosed mental illness.

Three professionals observe the group over a number of days, during which they complete tasks designed to expose signs of mental illness. One task involves performing stand-up comedy so the professionals can detect anxiety disorders. Horizon asks if you can tell who is who, and considers where the line between sanity and madness lies.