Hi Mike, I have a follow-up to Tsung's procD.allometry question -
If the initial HOS test is nonsignificant for (shape~size, ~group), but the following ANOVA table is significant for size and group effects, can one interpret that as differences in y-intercept but not slope? So basically the HOS test determined that the size:group interaction did not improve the model, and so removed it from the ANOVA formula? In that case, the ANOVA model is (shape~size+group), correct? That makes perfect sense looking at the output graphs, but I just want to be sure. And if one wanted to then determine which groups differed in y-intercept, would one set up the advanced.procD.lm model like this and compare the pairwise LS means? advanced.procD.lm(Y ~ size, ~ size+group, groups = ~group, slope = NULL, iter=10000) Thanks if you can confirm that I'm setting this up correctly, Christy On Thursday, December 8, 2016 at 7:37:33 PM UTC+11, Tsung Fei Khang wrote: > > Hi all, > > I would like to use procD.allometry to study allometry in two species. > > I understand that the function returns the regression score for each > specimen as Reg.proj, and that the calculation is obtained as: > s = Xa, where X is the nxp matrix of Procrustes shape variables, and a is > the px1 vector of regression coefficients normalized to 1. I am able to > verify this computation from first principles when all samples are presumed > to come from the same species. > > However, what happens when we are interested in more than 1 species (say > 2)? I could run procD.allometry by including the species labels via > f2=~gps, where gps gives the species labels. Is there just 1 regression > vector (which feels weird, since this should be species-specific), or 2? If > so, how can I recover both vectors? What is the difference of including > f2=~gps using all data, compared to if we make two separate runs of > procD.allometry, one for samples from species 1, and another for samples > from species 2? > > Thanks for any help. > > Rgds, > > TF > > > > > > -- 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.
