Comedians are able to make people laugh because they often display characteristics usually found in people with schizophrenia or bipolar disorder, research published on Thursday claims.

Their talent to amuse people lies in having unusual personalities and displaying what researchers say are high levels of psychotic characteristics, according to findings which appear to support the widely held belief of a link between madness and creativity.

The results are based on a study of how 523 comedians from the UK, USA and Australia described their own personalities and beliefs when they filled in a questionnaire measuring psychotic traits in people who are not troubled by mental illness.

"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," said Professor Gordon Claridge from Oxford University's department of experimental psychology. He is also one of the three co-authors of the findings, which are published in the British Journal of Psychiatry.

"Although schizophrenic psychosis itself can be detrimental to humour, in its lesser form it can increase people's ability to associate odd or unusual things or to think 'outside the box'. Equally, 'manic thinking', which is common in people with bipolar disorder, may help people combine ideas to form new, original and humorous connections," Claridge added.

In the study, the 404 male and 119 female comedians filled in a short online version of the Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE), which asks about schizophrenic and bipolar features. They included unusual experiences, which measures magical thinking, belief in telepathy and other paranormal events and a tendency to experience perceptual aberrations, as well as cognitive disorganisation, which captures distractability and difficulty in focusing one's thoughts.

It also covered introvertive anhedonia a reduced ability to feel social and physical pleasure as well as an avoidance of intimacy and impulsive non-conformity, the tendency towards impulsive, antisocial behaviour, which is often linked to a lack of mood-related self-control.

Comedians' scores were then compared to those of 364 actors and 831 people in non-creative occupations.

While the actors scored higher than the general group on three of the four measures, the comedians came out "significantly higher on all four types of psychotic personality traits" compared to them, the researchers reported. The actors emerged as not having introverted personalities, but the comedians did.

The researchers believe that the comedians' mindsets as revealed by their high ratings on all four counts helps to explain why they can entertain audiences.

Manic thinking, a feature of bipolar disorder, emerged as one of their key traits. "It is easy to see how this can account for the relationship between the manic side of bipolar disorder and comic performance," the authors say.

They cite the example of the late Spike Milligan, the comic and star of The Goon Show, who battled manic depression throughout his life. He "used the freely associating thought processes of his manic states to generate the zany humour and the wildly ridiculous ideas that were the hallmark of his depression".

Dr James McCabe, a senior lecturer in psychosis at the Institute of Psychiatry in London, said: "The comedians in this study rated themselves highly on divergent thinking, the ability to make connections between seemingly unrelated concepts. Humour theorists deconstruct jokes to work out what the elements are of successful or funny humour. According to this theory the juxtaposition of ideas from different mindsets are at the root of what people find funny about the joke."

However, the findings should not be taken as evidence of a link between comic talent and mental illness, said James McCabe, a senior lecturer at the Institute of Psychiatry in London.

The study had found an association between the thinking styles of comedians and mania, rather than psychosis in the sense that psychiatrists would use the term, he added.

Paul Jenkins, chief executive of the charity Rethink Mental Illness, said: "These are interesting findings, but we must make sure we guard against the 'mad creative genius' stereotype. Mental Illnesses like schizophrenia can affect anyone, whether they are creative or not. Our knowledge and understanding of mental illness still lags far behind our understanding of physical illnesses, and what we really need is much more research in this area."