variance partition in vegan
On Tue, May 27, 2008 at 05:30:15PM +0200, Alejandro Gonz?lez wrote:
I have recently used vegan package and I have shown that variance partition is also implemented. As I prefer to use R rather than CANOCO, I would like to know if results are strictly the same,
I don't think the results will be strictly the same. The vegan function varpart provides the unbiased estimators of the variation partitions, as described by Peres-Neto et al. 2006 (reference below). I could be wrong, but I think using CANOCO will provide the biased estimates.
because in some publications using this technique in CANOCO they only take into account significant variables according to MonteCarlo tests, and to my knowledge), with the vegan approach R does not do so.
I think the second part of your question is whether or not varpart incorporates variable selection? It doesn't, but there are several options available in R. The one closest to what CANOCO does is probably the packfor package, written by Stephane Dray (http://biomserv.univ-lyon1.fr/~dray/software.php). This package incorporates the improvements described by Blanchet et al. 2008 (manuscript at http://www.bio.umontreal.ca/legendre/reprints/index.html). So, if the results from vegan differ from Canoco it's because vegan uses improved techniques. If anyone knows different please let me know, as I'm spending a lot of time lately working with these functions! Cheers, Tyler @Article{peres-neto_legendre_ea_2006, author = {Pedro R. Peres-Neto and Pierre Legendre and St\'{e}phane Dray and Daniel Borcard}, title = {Variation partitioning of species data matrices: estimation and comparison of fractions}, journal = {Ecology}, year = 2006, volume = 87, number = 10, pages = {2614--2625} }
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