ok, but are there any requirements regarding sample size of individual groups? ______________________________________ Paul Van Daele Ghent University Evolutionary Morphology of vertebrates K.L. Ledeganckstr 35 9000 Gent T + 32 9 2645233 F + 32 9 2645344
Dance like nobody is watching Kiss like you have never been loved before ----- Original Message ----- From: "morphmet" <[EMAIL PROTECTED]> To: "morphmet" <[email protected]> Sent: Tuesday, February 13, 2007 10:12 PM Subject: RE: Advice on IMP > For a conventional multivariate test of significance you need to have > a sufficient sample size so that the degrees of freedom of the > covariance matrix are equal to or larger (preferably much larger) than > the number of variables. With 17 landmarks you will have 2*17-4 shape > variables so you will need more than just 15 specimens (3 groups of 5 > give you just 3*(5-1) = 12 degrees of freedom). > > ========================= > F. James Rohlf > Distinguished Professor, Stony Brook University > http://life.bio.sunysb.edu/ee/rohlf > >> -----Original Message----- >> From: morphmet [mailto:[EMAIL PROTECTED] >> Sent: Tuesday, February 13, 2007 3:17 PM >> To: morphmet >> Subject: RE: Advice on IMP >> >> Hi, >> >> I was going to post the same question regarding problem number 1 >> last >> week. I was working with a small data set (N = 5 for each of three >> species within one species group of a genus) with 17 landmarks on >> fly >> wings. Two of the species are sibling species, so very similar. I >> worked around the problem by either reducing the number of landmarks >> to >> 5 (deleting "noisy" and very similar landmarks) or by increasing the >> sample size. >> >> I am curious about what is causing the problem, too. >> >> Ed >> >> ************************************* >> Edward A. Lisowski, Ph.D. >> WA Department of Agriculture >> Plant Protection, Pest Division >> [EMAIL PROTECTED] >> 509-225-2603 (ph) 509-454-7858 (fax) >> >> >> >> >> >> -----Original Message----- >> From: morphmet [mailto:[EMAIL PROTECTED] >> Sent: Tuesday, February 13, 2007 11:36 AM >> To: morphmet >> Subject: Advice on IMP >> >> Hi everybody! >> I am using geometric morphometrics in a study on mandibles of mice. >> I >> have encountered problems using programs in the IMP series, and I >> would >> be very grateful if somebody more experienced with these could give >> me a >> hint on what to do here: >> >> 1)I load an output file from CoordGen and a GroupList file into >> CVAGen. >> The program displays the landmarks but does not finish the analysis, >> instead posting an error message: ?The within-group sum of squares >> and >> cross products matrix is singular?. I have inspected both input >> files >> several times; I cannot find any error; they do also perform well in >> PCAGen. What does the message tell me about my data? >> >> >> >> >> -- >> Replies will be sent to the list. >> For more information visit http://www.morphometrics.org > > > > > -- > Replies will be sent to the list. > For more information visit http://www.morphometrics.org > -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
