I've got too much time on my hands and not enough mathmatical ability but the math for 2 occurances in the same space is quite well documented if a little head spinning. for 3 more cases there is less info, these two links point the way to anyone with a BIG calculator http://mathforum.org/dr.math/faq/faq.birthdayprob.html http://mathforum.org/library/drmath/view/56650.html meanwhile if you include adjacent streets I think you reduce the odds by a half, third or even by 9 hope that helps I'd love to know the odd of three in a street if someone can do the extra maths