Dear List, I followed the discussion of the prior task "PSW and MDS" and it was very interesting what Fred Bookstein replied to the outgoing posting regarding the use of MDS:
"My rationale for using MDS instead of PCA is (1) uneven sample sizes / missing data, (2) lack of replicate samples, (3) a more general interest in overall patterns/distributions in the data." Fred Bookstein replied: "Your "rationale for using MDS" is actually the list of reasons for using PCA, which in this specific context does PRECISELY what you are asking MDS to do!" Well, this brings up a question that I could not answer myself yet. Actually I'm not a professional biologist, but I am very much interested in morphometrics as part of systematic work. I have a data set of a total of 70 specimens with eight morphological characters recorded each. The number of specimens in each assumed OTU is not equal though! I have recorded ventrals, subcaudals, labials entering the eye, suboculars, loreals, prefrontals, parietals, and the presence/absence of a specific colour pattern (0= absent; 1=present). Data were standard normalized (mean=0; st.deriv.=1). I initially used NMDS to verify assumed OTUs and continued using PCoA. The question now is, can I use these methods for these data to identify morphological distinctions (identify new species/subspecies)? Thanks in advance, Wulf --- The data set looks something like this: [...] 267 65 3 0 1 1 1 1 259 67 2 1 1,5 2 1 0 258 69 3 0 1 1 1 0 269 70 3 0 2 2 1 0 263 62 3 0 2 2 1 0 271 68 3 0 2,5 2 1 0 274 67 3 0 3 2 1 0 265 63 3 0 2 2 1 0 278 72 3 0 1 1 2 1 278 71 3 0 1 1 2 1 277 70 3 0 1 1 2 1 273 70 3 0 1 1 2 0 270 71 3 0 1 1 2 0 267 65 3 0 1 1 1 0 269 64 3 0 1 1 1 0 [...] -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
