Comedians have personality types linked with psychosis, like many other creative types, which might explain why they can entertain, researchers claim.They score highly on characteristics that in extreme cases are associated with mental illness, a study by Oxford University researchers suggests.Unusually, they have high levels of both introversion and extroversion.The team says the creative elements needed for humour are similar to traits seen in people with psychosis.The idea that creativity in art and science is connected with mental health problems has long captured public imagination.However, there has been little research on whether comedians have some of the traits–in a healthy form–associated with psychosis (delusions that can be present in schizophrenia and bipolar disorder).The researchers found that comedians scored significantly higher on all four types of psychotic personality traits than the general group, with particularly high scores for both extroverted and introverted personality traits.The researchers believe this unusual personality structure may help explain the ability of comedians to entertain. Prof. Gordon Claridge, of the University of Oxford’s Department of Experimental Psychology, said: "The creative elements needed to produce humour are strikingly similar to those characterising the cognitive style of people with psychosis, both schizophrenia and bipolar disorder.”He said although schizophrenic psychosis could be detrimental to humour, in a lesser form it could increase ability to associate odd or unusual things or to think "outside the box”.