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
