GENEALOGY-DNA-L Archives

Archiver > GENEALOGY-DNA > 2005-03 > 1110081148


From: "John A. Blair" <>
Subject: Re: FTDNATip TMRCA Tables
Date: Sat, 05 Mar 2005 22:52:47 -0500
References: <200503060118.j261Igqj007155@lists5.rootsweb.com>
In-Reply-To: <200503060118.j261Igqj007155@lists5.rootsweb.com>


Carol,

This just means that as we get more information on how two people are
related the probabilities change. The probabilities in the tables assume no
prior knowledge. The best way to show this is with an example.

I match another participant in my surname project on 23 of 25 markers.
According to FTDNATip:
"In comparing 25 markers, the probability that John A. Blair and ZZZZZZZZ
Blair shared a common ancestor within the last... "
....100 years.....200 years.....300 years.....400 years.....500
years.....600 years
.......is............is............is............is............is............is
......7.01%........26.47%........48.65%........67.06%........80.10%........88.49%
These probabilities are based on the specific two markers we mismatch on
and assumes we do not have any other information on when we might share a
common ancestor.

However this other participant and I KNOW that we DO NOT share a common
ancestor in at least four generations. When we factor the 4 generations
into FTDNATip we get the following new probabilities:
....100-200 years....300 years....400 years....500 years....600
years....700 years
.......is...............is...........is...........is...........is...........is
.....17.84%...........41.05%.......61.49%.......76.42%.......86.23%.......92.24%

I hope this answers your question.

John
-----
John A. Blair
Goffstown NH
http://blairgenealogy.com
mailto:
BLAIR DNA Project Coordinator




At 08:18 PM 3/5/2005, Carol wrote:

>John:
>I'm confused about what the last line of your table means:
>"The above probabilities assume that the participants have NO prior
>knowledge of how they might be related."
>
>Why does the 'probability' depend on the participants not knowing
>beforehand how they might be related?
>
>Carol Vass


This thread: