Hi Keith, First, under the standard formulation of the birthday problem, we want the same birthday to occur 3 or more times (your first inclination). Second, consider the case of 6 people, where 3 pairs of people have different birthdays (ie, 2 people share Jan 1st, 2 share March 1st, 2 share May 1st). Your function would return a false positive here. (That was just a simple example--this kind of problem would happen very frequently in a large group. With 50 people, the probability of getting at least one false positive is over 0.7...) Hope this helps, John (My apologies if this went out twice--I had to resend from my FAS account. Can someone let me know via private email if two copies of this email were sent to the list? Thanks.) On Feb 20, 2008 2:11 PM, Keith Schnakenberg <keith.schnakenberg at gmail.com> wrote: On question 2a, do we want to know the if the same birthday occurs three or more times, or if thee or more people share a birthday with at least one other person? In other words, does "(length(unique (room)) < people - 1) contain the information that we need to know? Thanks, Keith _______________________________________________ gov2001-l mailing list gov2001-l at lists.fas.harvard.edu http://lists.fas.harvard.edu/mailman/listinfo/gov2001-l _______________________________________________ gov2001-l mailing list gov2001-l at lists.fas.harvard.edu http://lists.fas.harvard.edu/mailman/listinfo/gov2001-l