Hi I am not sure if this question if appropriate for this forum but here it goes. I was trying to do PCA analysis using the multiv library and I realized that this particular library contains 8 methods of PCA which use different correlation covariance structures and normalization of the data. When I analyze one particular data set with the 8 different methods I get different results in terms of the graphical display and percentage of the variance explained. My question which method is more appropriate under what circumstances. If somebody knows a reference that talks about the 8 different methods mentioned in documentation of this library please let me know. I am familiar with the differences between a correlation and a covariance matrix, but not with the other ones. If you think that I should post this message in a different mailing list, please let me know. Thanks and apologies if there is any information in the archives that I did not find :-). Hector H?ctor L. Ayala-del-R?o, Ph.D. Center for Microbial Ecology & Center for Genomic and Evolutionary Studies on Microbial Life at Low Temperatures Michigan State University 545 Plant & Soil Sciences Building East Lansing, MI 48824-1325 Phone: 517-353-9021 Fax: 517-353-2917