GENEALOGY-DNA-L ArchivesArchiver > GENEALOGY-DNA > 2003-11 > 1067957596
Subject: [DNA] Puzzling Result: Statistician Needed?
Date: Tue, 4 Nov 2003 09:53:16 EST
A hard-to-fathom result has occurred recently in our BROWN surname study. I
believe it's unlike anything seen previously in the project, or anything I've
noticed in the discussions on this list.
The background is that participant B joined the project primarily to test the
proposition that his BROWN line was related to that of participant A. People
researching the two families thought they had very strong "paper trail"
evidence suggesting a common BROWN ancestry, and they even thought they could see a
physical resemblance between members of the two lines.
When B's results came back, however, he scored only 9/12 with A -- meaning
it's highly unlikely the two men share a recent common ancestor, according to
the statistical rules almost everybody uses in DNA genealogy.
Of course I realize such results happen all the time, that is, when a DNA
mismatch shows "no relation" between people who had thought they were related.
But here's the puzzle in the case at hand: Out of 54 unique haplotypes found
so far in our project (excluding B's own haplotype), B scored closer to A's
haplotype than he did to any other haplotype in our project!
If we assume A and B are not closely related, then I submit that B has an
equal chance of being "closest" to EACH AND EVERY participant in our project.
Under these assumptions, I calculate the probability at just over 98% that B
should be closer to somebody other than A.
(In other words, the a priori odds were 54-to-one AGAINST the result that was
actually found -- if the men did not have a recent common ancestor in their
Conclusion: It seems to me that the hypothesis of "no close relation" between
B and A is falsified at approximately the 98% confidence level.
I'm strictly an amateur in such matters, and my last graduate statistics
course was 40 years ago. So if there's a logical flaw in my reasoning, let the
Jim Brown, Co-Administrator
Brown DNA Study