Thank you very much for your advice. I'll try it. Now we are working with geometric morphomerics too, in order to compare different technique results. All the best, Lola
<>< <>< <>< <>< <>< <>< <>< <>< Dolores Garabana Barro Institute of Fisheries Research Eduardo Cabello, 6 36208 Vigo (Spain) e-mail: [EMAIL PROTECTED] ><> ><> ><> <>< ><> ><> ><> ><> ----- Original Message ----- From: <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, February 13, 2004 2:00 PM Subject: Re: Burnaby's method and discriminant analysis tolerance > I don't really remember the details of what the Burnaby scale-adjustment > does, but I think it's somewhat similar to Darroch and Mosimann's > approach to scale adjustment (someone correct me if I'm wrong). With > D&M, the measurements are transformed by dividing through by some > reasonable measure of size (for example, the geometric mean of all the > distances). If Burnaby and D&M are similar in what they do to the data, > you're probably having problems with discriminant analysis because your > variance-covariance matrices are singular (rank = number of measurements > - 1) and can't be inverted. Darroch and Mosimann describe how to get > the discriminant function scores out when using their brand of scale > adjustment. > > Darroch JN and Mosimann JE (1985) Canonical and principal components > of shape. Biometrika 72: 241-252. > > I hope this helps. > > Tim Cole > > > > At 12:21 PM 2/11/2004 -0500, you wrote: > >Have anyone had problems with the tolerance in discriminant analysis if > >the input variables for such anlaysis have previously been transformed > >by Burnaby's method? > > > >We are studing the population structure of a fish species in the North > >Atlantic. > >17 variables (distances between landmarks) have been measured for each > >fish , following the truss network model and in adition we have > measured > >some other structures as eye diameter, fin lengths, etc. We have 4391 > >cases, distributed in seven geographical locations. In order to > >eliminate the size influence, we have used two methods, i.e., residuals > >against standart length, and the Burnaby's method. > > > >Once we have removed the size effect, we run a discriminant analysis to > >observe differences between areas. We have no problem if we use the > >residuals as input for the discriminant analysis. But we cannot perform > >a discriminant analysis using as input the Burnaby's transformed > >variables, because we have problems with the tolerance of the > variables: > >the matrix is ill-conditioning. > > > >The problem doesn't seem to be in a particular variable or in a group > of > >data (data has been carefully screened for outliers). Simply, there is > >some redundancy. However the correlations between variables are not > >particularly high. > > > >We have also study if the problem is in the data, running the > >Discriminant Analysis with different combinations of the seven > locations > >we have. But the results don't give us a clue. > > > >For example, when doing the analyses with four locations (a-d), it > >works. But as soon, as you introuduce some of the other three (e-g), it > >fails. However, some combinations of e, f or g, with other locations it > >works. Thus, not neccessarily the problem is in the locations e-g, but > >when these locations are together with some other, but there is no > clear > >pattern. > > > >The same thing occurs with the variables. We have removed the variable > >than enter at last step (when tolerance drops below the limit), but > then > >is another variable which cause problems, and if removed is another one > >and so on. > > > >We suspect that the problem is relared with the way that burbany method > >estimate the transformed variables. Can anyone help us? > >Thanks in advance, > >Lola > > > ><>< <>< <>< <>< <>< <>< <>< <><=20 > >Dolores Garabana Barro > >Institute of Fisheries Research > >Eduardo Cabello, 6 > >36208 Vigo (Spain) > >e-mail: [EMAIL PROTECTED] > > ><> ><> ><> <>< ><> ><> ><> ><> > >== > >Replies will be sent to list. > >For more information see > http://life.bio.sunysb.edu/morph/morphmet.html. > > > Theodore M. Cole III, Ph.D. > Department of Basic Medical Science > School of Medicine > University of Missouri - Kansas City > 2411 Holmes St. > Kansas City, MO 64108 > USA > > Phone: (816) 235 -1829 > FAX: (816) 235 - 6517 > e-mail: [EMAIL PROTECTED] > www: http://c.faculty.umkc.edu/colet > == > Replies will be sent to list. > For more information see http://life.bio.sunysb.edu/morph/morphmet.html. > == Replies will be sent to list. For more information see http://life.bio.sunysb.edu/morph/morphmet.html.
