Subject: what is the probability of two people having the same name and birthday

I am researching matching demographic data in a database. To give an indication 
of the chances of incorrectly matching individuals with (say) different 
addresses, but the same name and birthday, can you estimate the likelihood of 
two individuals having the same name and birthday. What difference does it make 
if two of the three data elements of the birthday match (day, month, year), but 
the other one does not match.
Thanks

Re: what is the probability of two people having the same name and birthday