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Criticism
The scientific reality of parapsychological phenomena and the validity of parapsychological research is a matter of continued criticism. The methods of parapsychologists are regarded by some critics as a pseudoscience. Parapsychology does not have a clearly defined subject matter, an easily repeatable experiment that can demonstrate a psi effect on demand, nor an underlying theory to explain the paranormal transfer of information. James E. Alcock, professor of Psychology at York University, says that few of parapsychology's experimental results have prompted interdisciplinary research with more mainstream sciences such as physics or biology. As a result, parapsychology remains an isolated science to such an extent that its very legitimacy is questionable.

Fraud
There have been instances of fraud in the history of parapsychology research. Soal-Goldney experiments of 1941-43 (suggesting precognitive ability in subjects) were long regarded as some of the best in the field because they relied upon independent checking and witnesses to prevent fraud. However, many years later suspicions of fraud were apparently confirmed when statistical evidence, uncovered and published by other parapsychologists in the field, suggested that Dr. Soal had cheated by altering the raw data. Another parapsychologist, Walter J. Levi, Jr.'s also falsified experimental results. He was caught by J.B. Rhine and asked to step down from his position as director for the Institute for Parapsychology.

No scientific field is immune to instances of fraud or deception. However, parapsychologists have to be especially alert to deception on the part of their subjects. Fraud undoubtedly played a part in creating the positive reputations of Spiritualist mediums who were often caught in the act of duplicity. In the 1920s, magician and escapologist Harry Houdini said that researchers and observers could not create experimental procedures which absolutely preclude fraud. In 1979, magician and debunker James Randi perpetrated a hoax, now famously referred to as Project Alpha. Randi trained two young magicians and sent them under cover to Washington University's McDonnell Laboratory with the specific aim of exposing poor experimental methods and credulity thought to be common in parapsychology. Although no formal statements or publications from the McDonnell laboratory supported the likelihood that the effects demonstrated by the two magicians were genuine, both of Randi's trainees reportedly deceived experimenters over a period of four years with demonstrations of supposedly telekenetic metal bending. Such methodological failures have been cited as evidence that most, if not all, extraordinary results in parapsychology derive from error or fraud.

Criticism of experimental results
Although some critics feel that parapsychological study is scientific, they are not satisfied with its experimental results. Critics contend that apparently successful experimental results in psi research are more likely due to sloppy procedures, poorly trained researchers, or methodological flaws than to genuine psi effects. Many skeptics of parapsychology hold that the entire body of evidence to date is of poor quality and not properly controlled. They argue that the work is unscientific, partly because it lacks a framework within accepted scientific models, and partly because after decades of research it has not presented evidence that provides conclusive results. To explain the purported evidence for psi, skeptics often cite instances of fraud, flawed or potentially flawed studies, a psychological need for mysticism, and cognitive bias as ways to explain parapsychological results.

Because psi is a negatively defined concept, a typical measure of the evidence for such phenomena in parapsychological experiments is statistical deviation from chance expectation. However, critics point out that any statistical deviation from chance is, strictly speaking, only evidence of a statistical anomaly, or that some unknown variable was causing the deviation from chance. Ray Hyman contends that even if experiments could be made to reproduce the findings of certain parapsychological studies under specificed conditions, this would be a far cry from concluding that psychic functioning has been demonstrated. Assuming that something paranormal is occurring when other normal processes could account for the effect is considered a logical fallacy.

Controversy over meta-analytic techniques
A popular statistical technique called meta-analysis has been used by parapsychologists as a way synthesizing large bodies of work. The statistical power generated from combining the data from many studies is used to demonstrate evidence for anomalous effects. The popularity of meta-analyses in psi research has been criticized by numerous researchers, and is often seen as troublesome even within parapsychology itself. Critics contend that the practice of meta-analysis is post hoc. The evaluation of the metholological quality of a study, after it is done and the results are known, can create opportunity for biases to affect the analyses. Various strategies, methods and criteria can be selected, which provide an opportunity for selecting outcomes that are consistent with the expectations of the analyst. It is not uncommon to find that two or more meta-analyses done at about the same time by investigators with the same access to the literature reach incompatible or even contradictory conclusions.

Selective reporting has also been offered by critics as an explanation for the results of meta-analyses. This is sometimes referred to as a "file drawer" problem. A "file drawer" problem arises when only positive study results are made public, while studies with negative or null results are not made public. For example, a recent meta-analysis combined 380 studies on psychokinesis, including data from the PEAR lab. It concluded that although there is a statistically significant overall effect, it is not consistent and relatively few negative studies would cancel it out, so biased publication of positive results could be the cause.