[R-sig-phylo] Blomberg K Statistic

dwelsh at life.illinois.edu dwelsh at life.illinois.edu
Fri Jan 20 02:53:20 CET 2012

  I'm using the Picante package in R to calculate the Blomberg K.  I'm
trying to test for a phylogenetic signal in my data.  I'm using a
dataset with the PC score for 21 different species on a tree with
varying branch lengths.  I did this using the code here:

  I got a K statistic of 0.0006457603 and yet the resultant PIC.variance.P
is 0.001.  If I'm correct, the PIC.variance.P is the p-value and
significant at 0.05.  Is that correct?
  I then decided to play with my data and set all branch lengths equal to
1 to see how that would affect things.  I got a K statistic of 2.921763
and a PIC.variance.P value of 0.001.  My understanding is that K
statistics close to 0 are not significant and become significant close
to and above 1.
  I'm confused why I got a significant p-value for both K statistics, even
though one is very close to 0 (0.00065) and the other is above 2.  I
would appreciate any help in explaining Picante and the K statistic. 
Thank you.


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Daniel P Welsh
PhD Candidate
Teaching Assistant
Department of Animal Biology
University of Illinois at Urbana-Champaign
202 Shelford Vivarium
606 E. Healey Street
Champaign, IL 61821
lab phone: (217) 333-5323

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