Ted wrote --
> Based on zillions of BM simulations we have done with DOS PDSIMUL,
> you should never see a shift in mean value (versus starting value
> at root of tree), unless you are intentionally modeling a trend.
> Something must be wrong.
in response to Dean Adams:
>> For these simulations I generate a tree (in this
> case a
>> perfectly-balanced tree) and simulate 100 data sets on the same
>> phylogeny using a particular initial BM rate parameter (sigma).
...
>> However, the most curious finding is that for all methods, as sigma
>> increases, so too does the mean trait value across the tips (and
> the
>> converse occurs as sigma decreases). This observation is curious to
> me,
>> as one should not see a predictable shift in the mean under
> Brownian
>> motion.
Is it possible that the simulation is doing Brownian Motion on some
other scale, such as a log scale? If one does BM on the logs and then
looks at the original phenotype scale, you *would* expect that as the
variance among species increases, so does the mean of the species
means.
Joe
----
Joe Felsenstein j...@gs.washington.edu
Dept of Genome Sciences and Dept of Biology, Univ. of Washington,
Box 5065, Seattle Wa 98195-5065
[[alternative HTML version deleted]]
_______________________________________________
R-sig-phylo mailing list
R-sig-phylo@r-project.org
https://stat.ethz.ch/mailman/listinfo/r-sig-phylo
