Dear Nicole In a recent paper of mine, I have also dealt with both allometry and phylogeny, in a different way than Prof. Dean suggests. You might want to have a look; it might give you some ideas. Here is the link: http://link.springer.com/article/10.1007%2Fs13127-015-0238-2. Let me know if you do not have access and I will send you a PDF.
Best wishes, Anneke van Heteren 2016-02-02 19:26 GMT+11:00 Adams, Dean [EEOBS] <dcad...@iastate.edu>: > Nicole, > > > > There is no need to perform multiple residual-based analyses. If you wish > to obtain shape residuals where both the phylogeny and allometry (size) > have been taken into account, these are found as residuals from the PGLS > analysis: shape~size|phylogeny. > > > > However, a question then is what will these size/phylogeny shape residuals > be used to investigate? If the intention is to then evaluate these > relative to some other factor (say groups), then the correct approach is > just to perform a factorial PGLS analysis, where: shape~size+factor | > phylogeny (shape is a function of size and some other factor, given the > phylogeny). Additionally, if that factor describes groups, you may wish to > include the size:group interaction term. > > > > In fact, if that is indeed the case, it is advisable NOT to perform the > analysis in piecemeal fashion, where residuals from one regression are then > used in a subsequent linear model to test other effects. The reason is that > if there is some interaction between model effects (say, between size and > groups), then the residuals from the first regression are not correctly > capturing the observed patterns of variation. This is the multivariate > equivalent of the ANCOVA problem, and why an ANOVA on residuals from a > regression is not always the same as performing the ANCOVA analysis. The > best solution is to simply perform the factorial model, and account for > size while examining other effects. For this correct approach, one simply > requires software that allows one to perform factorial PGLS. Geomorph (and > as I recall, NTSYS) will allow uesrs to perform factorial PGLS. > > > > Hope this is helpful. > > > > Dean > > > > Dr. Dean C. Adams > > Professor > > Department of Ecology, Evolution, and Organismal Biology > > Department of Statistics > > Iowa State University > > www.public.iastate.edu/~dcadams/ > > phone: 515-294-3834 > > > > *From:* Nicole Dzenowski [mailto:ndzenow...@gmail.com] > *Sent:* Monday, February 1, 2016 9:18 PM > *To:* MORPHMET <firstname.lastname@example.org> > *Subject:* [MORPHMET] Questions regarding correction for allometry & > evolutionary allometry > > > > > Hi everyone, > > > > I had some questions regarding allometry correction. I'll be working with > closely related specimens on a project where I think a moderate chunk of > the shape variation is due to allometric size differences. Should (or can) > I correct for both, as in, regress shape on size and take the residuals and > then use a phylogenetic comparative method on those residuals and the size > data and then do another multivariate regression and then use the residuals > from that final regression as my new shape variables? > > > > Any help or direction is greatly appreciated. > > > > Thanks! > > -- > MORPHMET may be accessed via its webpage at http://www.morphometrics.org > --- > You received this message because you are subscribed to the Google Groups > "MORPHMET" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to morphmet+unsubscr...@morphometrics.org. > > -- > MORPHMET may be accessed via its webpage at http://www.morphometrics.org > --- > You received this message because you are subscribed to the Google Groups > "MORPHMET" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to morphmet+unsubscr...@morphometrics.org. > -- MORPHMET may be accessed via its webpage at http://www.morphometrics.org --- You received this message because you are subscribed to the Google Groups "MORPHMET" group. To unsubscribe from this group and stop receiving emails from it, send an email to morphmet+unsubscr...@morphometrics.org.