How can you tell if you have ESP?

The  subject of Extra Sensory Perception (ESP) came up in my class recently. According to a 2001 Gallup Poll, about 50% of the U.S. population believe in ESP. Few of my students were willing to admit publicly that they believe they can predict the future. Nonetheless, we had a spirited conversation about how to figure  out how you can be sure that you can predict the future.

ESP and my decision to study judgment and decision making

While I was contemplating graduate programs, I was inspired by Thomas Gilovich’s book,  How we know what isn’t so: The fallibility of human reason in everyday life. Gilovich, a professor at Cornell, dedicates a chapter to explaining how people come to believe they can predict the future. He points out how easy it is easy to arrive at such a conclusion – by collecting data. The idea was appealing and stuck with me.

The key issue  is that people tend to pay more attention to the times they are correct rather than the times they are incorrect. Imagine you wake up from a bad dream in which a friend has something bad happen to her. You call her and she tells you that she was just involved in a fender bender. Wow, you think, I must have ESP! The correct prediction (Say Bad/Is Bad) is exciting and memorable, and the same holds for situations in which you make correct predictions about good things (Say Good/Is Good).

Collect the data!

But to be sure that your ESP is a real phenomenon, you would need to compare the frequency of correct predictions, which are exciting and memorable, to the frequency of incorrect predictions (Say Bad/Is Good and Say Good/Is Good), which are less exciting and less memorable. Only when you have the data can you be sure that your experiences are not just coincidence.


If you like this post, you may want to check out a debate in the social psychology literature on whether ESP-like phenomena can be detected in lab settings. In short, the exchange points out that difficulties with the methods of data collection.

The fruit fly of Psi research

On one hand, Daryl Bem and Charles Honorton say that these effects exist in their paper, Does Psi Exist? Replicable Evidence for an Anomalous Process of Information Transfer, published in Psychological Bulletin.

Most academic psychologists do not yet accept the existence of psi, anomalous processes of information or energy transfer (such as telepathy or other forms of extrasensory perception) that are currently unexplained in terms of known physical or biological mechanisms. We believe that the replication rates and effect sizes achieved by one particular experimental method, the ganzfeld procedure, are now sufficient to warrant bringing this body of data to the attention of the wider psychological community. Competing meta-analyses of the ganzfeld database are reviewed, 1 by R. Hyman (1985), a skeptical critic of psi research, and the other by C. Honorton (1985), a parapsychologist and major contributor to the ganzfeld database. Next the results of 11 new ganzfeld studies that comply with guidelines jointly authored by R. Hyman and C. Honorton (1986) are summarized. Finally, issues of replication and theoretical explanation are discussed.

Julie Milton and Richard Wiseman, on the other hand, point to their difficulties replicating Bem and Honorton’s effects in a paper titled, Does Psi Exist? Lack of Replication of an Anomalous Process of Information Transfer:

D. J. Bem and C. Honorton (1994) recently presented in this journal a set of ganzfeld extrasensory perception (ESP) experiments conducted by C. Honorton that appeared to support the existence of a communication anomaly. In this article, the authors present a meta-analysis of 30 ganzfeld ESP studies from 7 independent laboratories adhering to the same stringent methodological guidelines that C. Honorton followed. The studies failed to confirm his main effect of participants scoring above chance on the ESP task, Stouffer z = 0.70, p =.24, one-tailed; M effect size (z/N1/2) = 0.013, SD = 0.23. The new studies included replication attempts of 3 out of 5 internal effects reported as statistically significant by D. J. Bem and C. Honorton. Only 1 was confirmed, and the authors found that D. J. Bem and C. Honorton were mistaken in describing the original effect as being statistically significant. The authors conclude that the ganzfeld technique does not at present offer a replicable method for producing ESP in the laboratory.