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 -- MORPHMET may be accessed via its webpage at http://www.morphometrics.org To unsubscribe from this group and stop receiving emails from it, send an email to morphmet+unsubscr...@morphometrics.org.