Randomness and Coincidences: Reconciling Intuition and Probability Theory Presentation by Tom Griffiths (Stanford University, Psychology Department). Coauthored by Joshua Tennenbaum (Stanford University, Psychology Department). Wednesday October 23 at noon Center for Basic Research in the Social Sciences 34 Kirkland Street, Room 22 Lunch will be served. Abstract: People are notoriously bad at reasoning about chance. Our intuitions about randomness and coincidences seem to be inconsistent with the normative structure of statistics: events that are equally likely to arise by chance differ in their subjective randomness, and we consistently underestimate the probability of coincidences. I will argue that we can understand why these apparent errors arise by focusing on the evidence observations provide about the processes that generated them rather than their probability of occurring by chance. As part of this argument, I will present a simple Bayesian framework that gives predictions about both the extent to which a set of events will seem random, and the strength of coincidences. This framework accurately predicts behavior in a variety of contexts, suggesting that statistics might yet contribute to understanding our intuitions about chance. The Research Workshop in Applied Statistics is a forum for graduate students, faculty, and visiting scholars to present and discuss statistical innovations and applications in the social sciences. For more information, contact corr(a)fas.harvard.edu. The paper may be accessed at: http://www-psych.stanford.edu/~gruffydd/papers/random.pdf The presenter's email is: gruffydd(a)psych.stanford.edu