Colleagues,
I want to alert your attention to a new article on-line at Evolution (Adams and
Collyer 2015: doi:10.1111/evo.12596). In it we compare two approaches for
performing phylogenetic regression of high-dimensional shape data (one based on
PICs and another based on PGLS). We show that although the two methods produce
the same test statistics, the permutation procedures commonly employed with the
methods can produce largely divergent statistical results. We demonstrate that
randomization tests using PICs have unacceptably high type I error rates, and
can lead to incorrect statistical and biological inferences. We then discuss
the statistical reasons for this, explain why the permutation method
implemented in the PGLS-based procedure leads to correct statistical and
biological inferences, and explain how the permutation procedure for PICs can
be adjusted to provide appropriate results.
Best,
Dean
Dr. Dean C. Adams
Professor
Department of Ecology, Evolution, and Organismal Biology
Department of Statistics
Iowa State University
www.public.iastate.edu/~dcadams/<http://www.public.iastate.edu/~dcadams/>
phone: 515-294-3834
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