On 06/04/2010 09:40 AM, Consuelo Hermosilla wrote:
> Hummm, true, I got confused! Sorry!! I meant scatter.enfa.
> What I don't understand is the length of the arrows. The grid is d=2, 
> different from the grid set with the biplot of marginality and 
> specialization (d=0.5). In that case, the length make senses to me, 
> but I don't understand it in the scatter.enfa. They don't have the 
> same lenght /value as they have in the biplot. Do you understand me?

I do not understand you... The function scatter.enfa draws the biplot 
associated with the results of the ENFA. The following paper explains 
this graph in detail:

Basille, M., Calenge, C., Marboutin, E., Andersen, R. and Gaillard, J.M. 
2008. Assessing habitat selection using multivariate statistics: some 
refinements of the ecological niche factor analysis. Ecol. model. 211: 
233--240.

The point on the X-axis of the graph returned by scatter.enfa is the 
centroid of used resources (the centroid of available resources 
correspond to the origin of the axes). The arrows on this graph 
correspond to the scores of the environmental variables on the axes of 
the ENFA (e.g. the coordinate of the arrow labelled "foo" on the X-axis 
correspond to the score of the variable "foo" on the marginality axis, 
and the coordinate on the Y-axis corresponds to the score on the first 
specialization axis).

I am not sure what you mean by "biplot of marginality and 
specialization". There is only one way to draw a biplot with the ENFA: 
it is provided by scatter.enfa (see the paper cited above). So I do not 
understand how the result of scatter.enfa could be inconsistent with the 
biplot, since the result of scatter.enfa *is* the biplot.
Best,

Clément Calenge

-- 
Clément CALENGE
Cellule d'appui à l'analyse de données
Office national de la chasse et de la faune sauvage
Saint Benoist - 78610 Auffargis
tel. (33) 01.30.46.54.14






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