Understanding uncertainty: ESP and the significance of
significance Is there such a thing as extra-sensory perception?
Image: Boston. In March 2011 the highly respected Journal of
Personality and Social Psychology published a paper by the
distinguished psychologist Daryl Bem, of Cornell University in
the USA. The paper reports a series of experiments which, Bem
claims, provide evidence for some types of extra-sensory
perception (ESP). These can occur only if the generally accepted
laws of physics are not all true. That's a pretty challenging
claim. And the claim is based largely on the results of a very
common (and very commonly misunderstood) statistical procedure
called significance testing. Bem's experiments provide an
excellent way into looking at how significance testing works and
at what's problematic about it. Bem's experiments and what he
did with the data Bem's article reports the results of nine
different experiments, but for our purpose it's sufficient to
only look at Experiment 2. This is based on