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From: Ann Turner <>
Subject: [AUTOSOMAL-DNA] Kimberly Powell blog post on AncestryDNA
Date: Tue, 15 May 2012 10:49:01 -0700


http://genealogy.about.com/b/2012/05/15/autosomal-dna-testing.htm?nl=1

I want to post something sometime in that very interesting long thread
about GEDCOM files, but this article mentions finding close connections at
all three autosomal testing services. Quoting Kathy Johnston from that
thread

"5. Even if I go back 4 generations, am I likely to randomly match any true
3rd cousins? NO!! because you need a database of over a million to find
that one in a million 3rd cousin. Even if you have more than 300 3rd
cousins alive today, there are over 300 million people living in the U.S.
Does FTDNA test that many people? No."

I have got to think more about the statistics here. Obviously we are going
to hear a disproportionate number of success stories, just because they're
so much fun. But it strikes me that we are hearing too many stories for the
one-in-a-million number to hold true. I have a 2nd cousin once removed at
23andMe who tested because his daughter worked at Illumina and got a free
kit. I tested a known cousin at FTDNA, and when she got her results back,
she recognized the name of a 3rd cousin once removed from another side of
her family.

I do think FTDNA overcalls the 3rd cousin bin, relying too much on the
length of the longest segments. Confirmed 3rd cousins tend to have multiple
segments over 5 cM in length. But why are we seeing so many stories about
confirmed close cousins? Just thinking out loud here -- maybe this is
related to the "birthday paradox":

http://en.wikipedia.org/wiki/Birthday_problem

Ann Turner


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