Archiver > GENEALOGY-DNA > 2011-01 > 1294171029

From: Dienekes Pontikos <>
Subject: Re: [DNA] How old is Y-Chromosome Adam?
Date: Tue, 4 Jan 2011 21:57:09 +0200
References: <><><><00e301cbac30$3bb02b80$c2482dae@Ken1><><010e01cbac34$c3983480$c2482dae@Ken1>
In-Reply-To: <010e01cbac34$c3983480$c2482dae@Ken1>

If the median gives 69% of the average mutation rate, then that would
result in both slower and faster markers producing greater ages using
median-/average- mutation rates, by the same scale factor (1/0.69).
Thus, the problem of the discrepancy between the two remains.

The thing to show is that the median/average mutation rate estimate
ratio decreases with higher mutability. Then you can quantify how much
of the 10+ fold difference in age estimates between the slowest and
fastest markers can be attributed to the postulated bias, and would
disappear if the average of the posterior distribution was taken.

On Tue, Jan 4, 2011 at 7:28 PM, Ken Nordtvedt <> wrote:
> ----- Original Message -----
> From: "Dienekes Pontikos" <>
>> That's not a problem for Ballantyne et al.'s mutation rate estimates
>> as they do not use the most likely value as the point estimate of the
>> marker mutation rate, but rather the median of the posterior
>> distribution, i.e., it is 50% probable for the mutation's rate to be
>> higher and 50% lower than the point estimate.
> That's better, but I wonder why Ballantyne did not just bite the bullet and
> use average value of posterior distribution?
> For seeing no mutations in N tries, average value of inferred distribution
> would be 1/N while median would be .69 / N if I did the math correctly.
> This of course assumes flat priors over the central bulk of the posterior
> distribution.
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