Dear Probability subforum, I have hard time thinking through how 11% is calculated. Anyone have any ideas? From "Thinking fast and slow" Kahneman. p 154 "...If you believe 3% of graduate students are enrolled in computer science (the base rate), and you also believe that the description of Tom W is 4 times more likely for a graduate student in that field than in other fields, then Bayes's rule says you must believe that the probability that Tom W is a computer scientist is now 11%. If the base rate had been 80%, the new degree of belief would be 94.1%. And so on...." Description of Tom W is that of typical CS student.