GENEALOGY-DNA-L ArchivesArchiver > GENEALOGY-DNA > 2011-11 > 1322525761
From: Terry <>
Subject: Re: [DNA] Sigma for Variance
Date: Tue, 29 Nov 2011 11:16:01 +1100
Regarding your formula for "sigma", on the first slide of your PowerPoint -
is that meant to be for a single STR marker?
Or is your formula for "sigma" meant to be for the standard deviation about
the TMRCA computed from a set of say 67 STR markers?
To me "sigma" should get a little better (smaller) if you used a few more
STR markers, but your formula seems to be independent of the number of STR
Also, your formula is surprisingly complex, so perhaps you could share your
On Sun, Nov 27, 2011 at 9:55 AM, Kenneth Nordtvedt
> A powerpoint file “Sigma for Variance” is now completed at
> http://knordtvedt.home.bresnan.net The first two slides summarize the
> analytically determined formulas for the distribution sigmas accompanying
> tmrca estimates for y trees under our simple models of STR mutation
> behavior. These formulas were confirmed as correct using hundreds of
> thousands of simulations. For those not so interested in the underlying
> derivations of sigma sizes, the last three slides in
> “Sigma for Variance” give some numerical outcomes or formula results for a
> broad assortment of y tree types. Both some genealogical time frame
> examples and deep time frame examples are given.
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