[R] PCA or CA

[Paul Dennis]

Dear all

I have a data set for which PCA based between group analysis (BGA) gives significant results but CA-BGA does not.

I am having difficulty finding a reliable method for deciding which ordination technique is most appropriate. 

I have been told to do a 1 table CA and if the 1st axis is>2 units go for CA if not then PCA.

Another approach is that described in the Canoco manual - perform DCA and then look at the length of the axes.  I used decorana in vegan and it gives axis lengths.  I assume that these are measured in SD units. Anyway the manual say if the axis length is <3 go for PCA,>4 use CA and if intermediate use either. 

Are either of these approaches good/valid/recommended or is there a better method?

Thanks

Paul  
 		 	   		  
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