Jun 25, 2014

Bem is Back: A Skeptic's Review of a Meta-Analysis on Psi


James Randi, magician and scientific skeptic, has compared those who believe in the paranormal to “unsinkable rubber ducks”: after a particular claim has been thoroughly debunked, the ducks submerge, only to resurface again a little later to put forward similar claims.

In light of this analogy, it comes as no surprise that Bem and colleagues have produced a new paper claiming that people can look into the future. The paper is titled “Feeling the Future: A Meta-Analysis of 90 Experiments on the Anomalous Anticipation of Random Future Events” and it is authored by Bem, Tressoldi, Rabeyron, and Duggan.

Several of my colleagues have browsed Bem's meta-analysis and have asked for my opinion. Surely, they say, the statistical evidence is overwhelming, regardless of whether you compute a p-value or a Bayes factor. Have you not changed your opinion? This is a legitimate question, one which I will try and answer below by showing you my review of an earlier version of the Bem et al. manuscript.

I agree with the proponents of precognition on one crucial point: their work is important and should not be ignored. In my opinion, the work on precognition shows in dramatic fashion that our current methods for quantifying empirical knowledge are insufficiently strict. If Bem and colleagues can use a meta-analysis to demonstrate the presence of precognition, what should we conclude from a meta-analysis on other, more plausible phenomena?

Disclaimer: the authors have revised their manuscript since I reviewed it, and they are likely to revise their manuscript again in the future. However, my main worries call into question the validity of the enterprise as a whole.

To keep this blog post self-contained, I have added annotations in italics to provide context for those who have not read the Bem et al. manuscript in detail.

My review of Bem, Tressoldi, Rabeyron, and Duggan


Mar 26, 2014

Behavioral Priming: Time to Nut Up or Shut Up


In the epic movie "Zombieland", one of the main protagonists –Tallahassee, played by Woody Harrelson– is about to enter a zombie-infested supermarket in search of Twinkies. Armed with a banjo, a baseball bat, and a pair of hedge shears, he tells his companion it is "time to nut up or shut up". In other words, the pursuit of happiness sometimes requires that you expose yourself to grave danger. Tallahasee could have walked away from that supermarket and its zombie occupants, but then he would never have discovered whether or not it contained the Twinkies he so desired.

At its not-so-serious core, Zombieland is about leaving one's comfort zone and facing up to your fears. This I believe is exactly the challenge that confronts the proponents of behavioral priming today. To recap, the phenomenon of behavioral priming refers to unconscious, indirect influences of prior experiences on actual behavior. For instance, presenting people with words associated with old age ("Florida", "grey", etc.) primes the elderly stereotype and supposedly makes people walk more slowly; in the same vein, having people list the attributes of a typical professor ("confused", "nerdy", etc.) primes the concept of intelligence and supposedly makes people answer more Trivia questions correctly.

In recent years, the phenomenon of behavioral priming has been scrutinized with increasing intensity. Crucial to the debate is that many (if not all) of the behavioral priming effects appear to vanish like thin air in the hands of other researchers. Many of these researchers –from now on, the skeptics– have reached the conclusion that behavioral priming effects are elusive, brought about mostly by confirmation bias, the use of questionable research practices, and selective reporting.