Friday 13th is turning out to be unlucky for charlatans claiming to have psychic powers.

Richard Wiseman, senior lecturer in psychology at the University of Hertfordshire, and Robert Morris, Koestler professor of parapsychology at Edinburgh University, have today launched Guidelines for Testing Psychic Claimants, a book aimed at helping academics, police, cult investigators, health professionals and the media to examine claims objectively.

Many people claim to be psychic: palm readers claim they can look into the future, mediums claim to communicate with the dead, faith healers and psychic surgeons claim to cure illness and psychics have been used as business consultants, to attract followers to religious organisations, and to help solve crime.

The police, for example, are often unsure of what to do about psychic detectives, and the book could help them "weed out some of the duds", Dr Wiseman said.

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Researchers could also benefit from the book, since if parapsychologists had worked with a subject who was subsequently exposed as a fraud, and they had not realised they had been tricked, this could damage the reputation of individual academics and the discipline as a whole.

Simply having the book may be a protection against some frauds who will seek an easier target, Dr Wiseman said. It also warns against allowing claimants to weaken the testers' control, by complaining, for example, that video equipment makes them nervous, or insisting that participants hold hands in a darkened room -- which ensures that testers will not detect an accomplice in the darkness.

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Dr Wiseman is himself a prize-winning magician, specialising in close-up magic. He is an associate of the Inner Magic Circle which has a strict oath of secrecy, but it is acceptable to explain tricks to protect the public from scams.

"The good conjuring tricks are stunningly simple," he said.

Guidelines for Testing Psychic Claimants by Richard Wiseman and Robert L. Morris, University of Hertfordshire Press, Pounds 7.