American parapsychologist and associate of J B Rhine at Duke University, who is best known for his work with mediums and poltergeists and his contributions to experimental parapsychology.

In 1934 and 1935, while a graduate student working in Duke University’s Parapsychology Laboratory, Pratt was put in charge of studying mediumistic communications with Eileen Garrett. When he analysed his data Pratt found that it supported a paranormal interpretation. Later he refined his methods of evaluating verbal material delivered in trance by devising a procedure called the Greville method, where sitters score items as right or wrong for them and then all items are judged against each other. In 1958 Pratt was sent by Rhine to investigate the Seaford Poltergeist: the first poltergeist case to be studied by the parapsychology laboratory. Along with William Roll, Pratt invented the term ‘recurrent spontaneous psychokinesis’ to describe poltergeist cases.

From 1962 until his death Pratt served as president of the Psychical Research Foundation and in the 1970s he became a trustee of the American Society for Psychical Research. He died in November 1979. A few years earlier he had set a combination lock; he’d refrained from writing down the combination, lest anyone discover it, but every year he opened the lock using a mnemonic phrase. If he survived death his aim was to communicate this phrase through a medium, but to date the lock remains closed.