After 102 years of trying, scientists studying poltergeists, telepathy, and other psychic effects have yet to make their case that such effects exist. They have yet to produce convincing evidence that such paranormal phenomena exist, let alone that they have even a glimmer of what might underlie such phenomena.
But some of the better parapsychologists have significantly tightened their experimental procedures and raised their standards of evidence in recent years. So it's worthwhile listening when one of them warns about the need for informed skepticism in this field. It could be an antidote for the wide-eyed gullibility with which claims of paranormal ''discoveries'' often are reported by news media.
Stanley Krippner, a leading parapsychologist affiliated with the Saybrook Institute, laid out some of these caveats at a symposium on fringe science during the recent annual meeting of the American Association for the Advancement of Science (AAAS) in New York. He made the point that parapsychological phenomena ''are certainly a topic worthy of investigation.'' Yet he cautioned that the investigators ''should stress the speculative nature of our concepts, be candid about the controversial status of our field, and not make assertions which go beyond what is warranted by the evidence.''
The need for caution is evident in the frequent use of statistical tests as demonstrating that some paranormal effect has been observed. Usually there are no clear-cut results in experiments with such purported abilities as telepathy or psychokinesis (mental manipulation of physical objects or physical effects). Instead, results are cited as being significantly (or not significantly) better than what would have happened by chance.
But while parapsychologists may cite such evidence in good faith, as did Krippner in his AAAS paper, scientists in other fields may not be impressed. For example, James Alcock, a psychologist at York University in Toronto, points out all that such statistical analysis shows is a deviation from the experimenter's mathematical model of what he or she thinks would have been due to chance. He explains in the summer issue of The Skeptical Inquirer that, because the experimenters themselves decide what chance means, ''statistical conclusions cannot say anything at all about the existence or nonexistence of psi (psychic phenomena).''
Such disagreements about what constitutes valid evidence are likely to continue indefinitely. The point to be drawn from Krippner's remark is that claims by parapsychologists of evidence that couldn't have arisen by chance - and, especially, news reports of such claims - should be taken with a large grain of salt if they do not also recognize the controversial nature of the evidence.
Krippner offers a set of rules for improving parapsychologists' credibility and sharpening their scientific insight. Some of them are worth wider consideration, for they put claims of the paranormal in a useful perspective.
For example, he advises parapsycho-logists to ''abandon their revolutionary stance regarding their field.'' He adds that as long as they ''use orthodox scientific methodology their findings are, by definition, unrevolutionary.'' So much for the assertion that psychic phenomena represent a dimension beyond science.
Krippner warns against relying ''too heavily on so-called evidence from spontaneous cases or from data obtained in quasi-experimental settings (i.e., the work of 'psychic detectives').'' Such material, he says, ''is open to various kinds of flaws and overinterpretation.''
What is perhaps most important of all from the public's point of view, he warns against ''claimants who put forward untestable, unfalsifiable notions permeated with supernaturalism and metaphysics.'' Such claims may make headlines. But they are inherently unsound. ''Parapsychology,'' Krippner observes, ''needs to commit itself to intellectual self-discipline and critical judgment.''
Krippner also notes that ''claims of practical applications of psi should be treated with extreme caution.'' This is especially important when the claims involve the dubious practice of so-called ''psychic healing'' or ''psychic surgery'' and the use of clairvoyance to predict the ups and downs of commodity markets, to cite two notorious examples.
Krippner's advice is valuable. Psychic frauds and phonies abound. Even reputable parapsychologists are prone to wishful interpretation of their studies. And the media play up spurious claims.
For his part, Krippner does believe that parapsychologists have a worthwhile subject to investigate. He says too many people have had ''so-called psychic experience'' for this to be ignored. ''. . . the case for parapsychology is simply that an understanding of these reported experiences is worthy of significant research efforts,'' he declares.
That is a legitimate position to take, even though some mainstream scientists may disagree. However, when it comes to news reports of poltergeists or TV shows ''In Search of . . .'' gullible viewers, we all can share Krippner's healthy skepticism.