On May 1, 2013, at 8:37 PM, Thomas Parr wrote: > This is not a request for coding help so there is no reproducible code,
So this is a general statistical problem? Perhaps you should try: CrossValidated.com > > rather I am trying to figure out if anyone had had a similar experience. > > My question is related to partitioning the variance in rda (vegan) results > for multiple groups of variables. Sounds like a question for authors of the package. > I have a high dimensional dataset with > 79 explanatory variables and 9 response variables. Within those 79 > explanatory variables there are ~8 groups (e.g. water chemistry, land cover, > geography, surficial geology, etc). To partition out their unique and > binary interactive variance, I run the ~30 conditioned RDAs necessary to > determine the "pure effects" of each group and the "pure binary > interactions" of those groups with each other. > > My method for partitioning the variance of binary interactions is as > follows: > Inertia of the interaction of water chemistry and geography = inertia of the > combined effect (conditioned on the remaining groups) - Inertia of just > Waterchemistry - inertia of just geography. > > When I do this for each combination two problems arise: > 1. I get small negative numbers when 0 should be the lowest possible number. > Does this occur because of internal rounding in the RDA code, or is there > something else going on? And how exactly would one tell if there is no data? (or even results?) > (If Total inertia is 9 and explainable inertia is > 5.4, a "small negative number" for an interaction inertia might be -0.003 > after the above partitioning procedure.) > > 2. The sum of partitioned inertia is greater than the constrained inertia on > the full model (in this case Total Inertia is 9, explainable inertia is > 5.41, and the sum of partitioned inertia is 5.57). > Again... with no data. How would one explain this? > I have checked for coding errors. -- David Winsemius Alameda, CA, USA ______________________________________________ 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.
