Performing CVA on the first PC axes seems a good approach. However, using it, I have run into a problem as to how many PC axes to use and how to justify including the first 5, or 6, or 7? One way is to use no more PC than the number of specimens in a group, given that enough variation (90-95%) is included. Does that seem to make sense? Or should there be a more stringent criterion?
> I have a version of CVAGen that will first perform a PCA on the partial > warp scrores and uniform components, and then perform a CVA on a limited > number of the PCA scores. So if you have 20 variables in the data and > only 20 specimens, you might find that the first 5 or 6 PCA axes have > 90% or more of the variance, so that a CVA using only 5 or 6 PCA axes > might might produce reasonable results. This approach may be > particularly useful if you are using a lot of semi-landmarks. regards, Asta *** Asta Audzijonyte Finnish Museum of Natural History POB 26 (Teollisuuskatu 23) FI-00014 University of Helsinki www.fmnh.helsinki.fi/english/zoology/invertebrates/research/molecular/asta.htm vision without action is a daydream action without vision is a nightmare -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
