Hi Sergio.
We don't expect the residuals from PGLS to be independent draws from a
normal distribution, but multivariate normal with a correlation
structure given by the tree.
Here I give some more explanation of this on my blog:
http://blog.phytools.org/2013/02/a-comment-on-distribution-of-residuals.html.
Let us know if this is helpful.
All the best, Liam
Liam J. Revell, Assistant Professor of Biology
University of Massachusetts Boston
web: http://faculty.umb.edu/liam.revell/
email: [email protected]
blog: http://blog.phytools.org
On 4/18/2015 1:15 PM, Sergio Ferreira Cardoso wrote:
Dear all,
I'm performing PGLS's with an ultrametric phylogenetic tree (divergence
time as branchlengths). I tied Pagel's Lambda transformation, OU
transformation, regular GLS and OLS, to compare results. There is one
problem: the residuals of my analyses are not normal. I tried to remove big
outliers but it made things even worse, because without them there are even
more outliers.
So, what should I do? The results are consistent in both 4 tests. But can I
trust the results of the PGLS? Is it particularly bad if PGLS residuals
aren't normal? Does it critically afect my results?
Thanks in advance.
Best regards,
Sérgio.
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