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Archiver > DNA-R1B1C7 > 2007-08 > 1186894689


From: "David Ewing" <>
Subject: Re: [DNA-R1B1C7] Network.exe
Date: Sat, 11 Aug 2007 22:58:09 -0600


Ken Nordtvedt said, "If you fish long enough for the "right" set of markers
you will get the results you want. It is important to try to use a "hands
off" set of markers."

Well, yes. But surely you don't want to simply ignore that some markers are
much more volatile than others. And I think you would probably acknowledge
that comparing the results you get with several different alternative sets
of markers will illustrate the point you make. I think the trouble you warn
about would come from cherry picking markers and then not revealing that you
had done so.

I think that choosing to consider markers that have mutation rates less than
some cut-off point is not "fishing" or cherry-picking, it is simply trying
to reduce the noise introduced by volatile markers.

In my case, at least, there are no results I "want." What I do want is to
understand what the hell is going on, which I freely admit that I do not,
presently. There are lots of ways for us to deceive ourselves. The one I
have been trying to address in my recent postings is to believe TMRCA
prognostications without considering that these can differ by orders of
magnitude depending on what markers are used and what assumptions are made
about mutation rates and generation times.

Let me ask this. How, exactly, does one approach these questions with "hands
off?" There is no way around starting with a set of assumptions. Another way
to deceive oneself is to neglect noticing that someone has had a "hand" in
making these assumptions. Now, I recognize Ken Nordtvedt not only knows
this, he is capable of making quantitative formal statements of it, but I
feel compelled to argue that discussing these factors is not "fishing."

David Ewing

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