Hi All- The division involved in this particular formulation of CVA is by a pooled covariance matrix, so there is no direct limitation in the size of sample size within group imposed by this division. I would doubt this form of CVA will work terribly well if there are not enough samples within a group to make a reasonable estimate of the mean of the group.
-Dave H. David Sheets, PhD Chair,Dept of Physics, Canisius College 2001 Main St Buffalo NY 14208 >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 > -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
