Julie, There is an explanation for this on the following web page:
http://yudkowsky.net/bayes/bayes.html\ It is pretty deep in the page (after much discussion of urns that contain colored plastic eggs, some with pearls and some without), so have patience. For JDM wonks, this is a pretty neat page. The author has a bunch of Java applets that compute the probabilities for these problems combined with nice graphic displays. Good luck with your class! Claudia J. Stanny, Ph.D. Director, Center for University Teaching, Learning, and Assessment Associate Professor, Psychology University of West Florida Pensacola, FL 32514 - 5751 Phone: (850) 857-6355 or (850) 473-7435 e-mail: [EMAIL PROTECTED] -----Original Message----- From: Julie Osland [mailto:[EMAIL PROTECTED] Sent: Thu 4/3/2008 3:26 PM To: Teaching in the Psychological Sciences (TIPS) Subject: [tips] Bayes' Theorem Help Needed I used some of Scott Plous' quiz items in my Social Psych Class the other day, and I am in the process of integrating student answers into my lecture, along with feedback on the correct answers. One of the items is Imagine two urns filled with millions of poker chips. In the first urn, 70% of the chips are red and 30% are blue. In the second urn, 70% of the chips are blue and 30% are red. Suppose one of the urns is chosen randomly, and a dozen chips are drawn from it: eight red chips and four blue chips. What are the chances that the chips come from the urn with the mostly red chips? The answer given by Plous is 97%. He then references the fact that this involves Bayes' theorem and to see a chapter by Edwards (1968) in "formal representation of human judgment." We don't have this book, and I'd like to be ready for the student who asks me to show them how to arrive at this answer. Can anyone help me Thanks, Julie Osland Dr. Julie A. Osland, M.A., Ph.D. Assistant Professor of Psychology Wheeling Jesuit University 316 Washington Avenue Wheeling, WV 26003 Office: (304) 243-2329 e-mail: [EMAIL PROTECTED] --- To make changes to your subscription contact: Bill Southerly ([EMAIL PROTECTED]) --- To make changes to your subscription contact: Bill Southerly ([EMAIL PROTECTED])
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