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Archiver > GENEALOGY-DNA > 2003-11 > 1069442016


From: Charles <>
Subject: Re: [DNA] Genetic Distance calculation method -- which method ismost correct?
Date: Fri, 21 Nov 2003 14:13:36 -0500
References: <OF1A2B197A.A0F0DD49-ON85256DE3.007525EA-85256DE3.0078EBB1@downstate.edu> <REME20031119183221@alum.mit.edu> <3FBD7168.7000706@kerchner.com> <REME20031120224215@alum.mit.edu>
In-Reply-To: <REME20031120224215@alum.mit.edu>


John:

Re. Genetic Distance calculation/estimation. Using your "sum of the
squares of the differences" method vs. "simply adding up the
differences" method used by FamilyTreeDNA.com in their Y-DNA surname
group project tables of calculating/estimating Genetic Distance between
two people.

Again, for these examples let's ignore the markers which need special
attention such as multi-copy markers, etc., for counting differences. My
math method question is how does one add up the marker differences once
they have been determined for each marker.

Here is an example for discussion purposes:

Example 1:
If two people sharing the same surname in a surname project group differ
at three markers such that they differ at the three markers by 1 step at
each marker, then:

FamilyTreeDNA.com method says the Genetic distance is: 1+1+1 = 3

John Chandler method says the Genetic Distance is: (1*1)+(1*1)+(1*1) = 3

Example 2:
If two people sharing the same surname in a surname project group differ
at only one marker by 3 steps, then:

FamilyTreeDNA.com method says the Genetic distance is: 3 = 3

John Chandler method says the Genetic Distance is: (3*3) = 9

It doesn't make sense to me to emphasize/weight a 3 step difference at
one marker (whether or not they were three 1 step mutations over time or
a single one 3 step jump) much more than three 1 step differences at
three markers. The sum of the squares of the differences method makes a
3 step difference at one marker imply that the two people are three
times further apart in Genetic Distance as compared to two people who
have 1 step differences at three markers? John, you're a math and
statistics expert. I am not. Can you clarify more why your method for
calculating Genetic Distance is the correct one, using my above
examples? Can others please comment too. Thanks.

Charles






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