Defense attorneys interested in learning more about DNA statistics might find the following articles interesting because the “birthday problem” is analogous to looking for partial matches in a DNA database. The birthday problem is a classic puzzle that asks if you had a room full of people, how many people would you need in the room to make the odds of two people having the same birthday at least 50-50. Surprisingly, the answer is just 23.
In the “birthday problem,” when you do not designate a specific birthdate, you open up the opportunity for many pairs to be made from a much smaller sampling of people than if you specified a specific birthday. The same applies in with DNA when searching a DNA database for any set of matching loci, rather than looking to match a specific set of loci to another distinct set of loci.
This NY Times post is part a 6-part series entitled “Me, Myself and Math” and does a great job of explaining the birthday problem. For folks wanting more in-depth information about how the birthday problem is useful for understanding trawling of DNA databases for partial matches, take a look at this article by David H. Kaye.