Hi David, On Fri, May 8, 2009 at 10:27 AM, <dde...@sciborg.uwaterloo.ca> wrote:
> My questions are as follows; > > 1) can "raw" data be used to construct the dissimilarity matricies? or > should they be standardized? different variables have different measurment > scales, my inclination is to standardize, but I don't know if this will > dampen relationships between variables. I'd standardize, especially if you're using Euclidean distances. The Goslee and Urban JSS paper on the ecodist package goes into more detail (as do some of the references cited therein). > 2) If env1 and another variable are correlated, is the appropriate test > var1 ~ env1 + env2 + space?, > or > var1 ~ env1 + space and then var1 ~ env2 + space? Test for what? The first one partials out both env2 and space from the relationship of var1 ~ env1, a very different thing than the second example. > 3) interpretation... Does the value of "r" (i.e. + or -) imply spatial > overlap (+) or spatial exclusion (-)? A negative value for r is usually uninformative (unless you've used particular data transformations or something otherwise unusual). The Mantel test question is generally: do differences in X correspond to differences in Y, so the test you want is whether r > 0. Again, see the JSS paper discusses this further. Sarah -- Sarah Goslee http://www.functionaldiversity.org ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
