Cordón, Luis A., Popular psychology: an encyclopedia, Westport, Conn, Greenwood Press, 2005, p. 182, ISBN 0-313-32457-3.
«The essential problem is that a large portion of the scientific community, including most research psychologists, regards parapsychology as a pseudoscience, due largely to its failure to move beyond null results in the way science usually does. Ordinarily, when experimental evidence fails repeatedly to support a hypothesis, that hypothesis is abandoned. Within parapsychology, however, more than a century of experimentation has failed even to conclusively demonstrate the mere existence of paranormal phenomenon, yet parapsychologists continue to pursue that elusive goal.»
