Agreed! Similarly, Pagel's lambda ad Grafen's rho were designed from a purely statistical perspective, whereas OU and ACDC models are motivated by ties to a possible set of biological processes.
Cheers, Ted From: Alejandro Gonzalez Voyer [alejandro.gonza...@iecologia.unam.mx] Sent: Thursday, May 14, 2015 8:47 AM To: Theodore Garland Jr Cc: Sergio Ferreira Cardoso; R phylo mailing list mailing list Subject: Re: [R-sig-phylo] Non-ultrametric tree PGLS Hi Sergio, I would add to Ted’s reply that you are not only considering alternative statistical models but that the evolutionary assumptions from the models you are fitting also differ, and you need to keep this in mind when comparing models. Comparison of AICs or any other estimate of goodness of fit must also involve careful consideration of the assumptions of the models you are comparing. In your particular case, the tree with branch lengths set to equal values (all branch lengths = 1) implies different amount of time to evolve for each of your species (in other words the expected variances - diagonal terms in the variance-covariance matrix - differ between the species), and thus you should consider whether such an assumption makes biological sense in your system. Cheers Alejandro _______________________________________________ Dr Alejandro Gonzalez Voyer Laboratorio de Conducta Animal Instituto de Ecología Circuito Exterior S/N Ciudad Universitaria Universidad Nacional Autónoma de México México, D.F. 04510 México Tel: +52 55 5622 9044 E-mail: alejandro.gonza...@iecologia.unam.mx<mailto:alejandro.gonza...@iecologia.unam.mx> El 14/05/2015, a las 10:39, Theodore Garland Jr <theodore.garl...@ucr.edu<mailto:theodore.garl...@ucr.edu>> escribió: Hi Sergio, I am not quite understanding the situation nor why you see a "problem." if I understand correctly, you are considering these five (5) alternative models for some sort of simple or multiple regression: OLS = star phylogeny PGLS with real-time branch lengths (ultrametric) Pagel's lambda with real-time branch lengths (ultrametric) PGLS with all branch legnths equal to 1.0 Pagel's lambda with all branch lengths equal to 1.0 To help decide which model best fits your data, you can look at AIC or for some comparisons do a likelihood ratio test. My experience is that any of the transform models (Pagel's lambda, Grafen's rho, OU in various implementations, ACDC) can sometimes yield really bizarre results when you start with a non-ultrametric tree. You need to be careful and check the REML likelihood surface for multiple peaks, etc. Cheers, Ted Theodore Garland, Jr., Professor Department of Biology University of California, Riverside Riverside, CA 92521 Office Phone: (951) 827-3524 Facsimile: (951) 827-4286 (not confidential) Email: tgarl...@ucr.edu<mailto:tgarl...@ucr.edu> http://www.biology.ucr.edu/people/faculty/Garland.html http://scholar.google.com/citations?hl=en&user=iSSbrhwAAAAJ Director, UCR Institute for the Development of Educational Applications Editor in Chief, Physiological and Biochemical Zoology Fail Lab: Episode One http://testtube.com/faillab/zoochosis-episode-one-evolution http://www.youtube.com/watch?v=c0msBWyTzU0 ________________________________________ From: R-sig-phylo [r-sig-phylo-boun...@r-project.org] on behalf of Sergio Ferreira Cardoso [sff.card...@campus.fct.unl.pt] Sent: Thursday, May 14, 2015 8:32 AM To: r-sig-phylo@r-project.org Subject: [R-sig-phylo] Non-ultrametric tree PGLS Hello all, I have an ultrametric phylogenetic tree with divergence times as branch lengths. To see if there was a big difference between using these branch lengths and equal (=1) branch lengths I set all lengths to 1 and ran a PGLS. I ran with Lambda transformations and the estimation is that Lambda is superior than 1 (both with ML and REML estimation). I suppose this is a consequence of the tree being non ultrametric. Is there a solution for this problem or should I, in this case, just ran a GLS (Brownian Motion) to avoid the over estimation of the phylogenetic signal? Best regards, Sérgio. -- Com os melhores cumprimentos, Sérgio Ferreira Cardoso. -------------------- Best regards, Sérgio Ferreira Cardoso MSc. Paleontology candidate Departamento de Ciências da Terra - FCT /Universidade Nova de Lisboa Geociências - Universidade de Évora Lisboa, Portugal ᐧ [[alternative HTML version deleted]] _______________________________________________ R-sig-phylo mailing list - R-sig-phylo@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-phylo Searchable archive at http://www.mail-archive.com/r-sig-phylo@r-project.org/ _______________________________________________ R-sig-phylo mailing list - R-sig-phylo@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-phylo Searchable archive at http://www.mail-archive.com/r-sig-phylo@r-project.org/ [[alternative HTML version deleted]] _______________________________________________ R-sig-phylo mailing list - R-sig-phylo@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-phylo Searchable archive at http://www.mail-archive.com/r-sig-phylo@r-project.org/
