If that is the case then you may just want to add a constant value to all the data prior to entering them into the DF. Wouldn't that work? Clay
Clay E. Corbin, PhD 400 East 2nd Street Hartline Science Center Biological & Allied Health Sciences Bloomsburg University Bloomsburg, PA 17815 Phone: 570-389-4134 >>> <[EMAIL PROTECTED]> 2/13/2004 8:00:31 AM >>> 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.
