Hello, I have run a linear discriminant analysis for the simple 2 group case using the MASS package lda() function. With priors fixed at 0.5 and unequal n for each group, the output basically provides the group means and the LD1 value. There is no automatic output of the cutoff (decision boundary) value used to classify values of the response variable into the different groups. I have tried various unsuccessful approaches to extract this value. It is obvious that in the simple 2 group case the value will be close to the mean of the 2 group means and that the LD1 value is involved (perhaps grand mean * LD1?). I am probably missing (misunderstanding?) the obvious and would appreciate being educated in this matter. Thanks. Regards,BJ [[alternative HTML version deleted]]
This is not an R question. Post it on a statistics site like stackexchange, instead. http://stats.stackexchange.com/ -- Bert On Fri, Sep 23, 2011 at 9:49 AM, B Jessop <deelman@hotmail.com> wrote:> > > > > Hello, I have run a linear discriminant analysis for the simple 2 group > case using the MASS package lda() function. With priors fixed at 0.5 and > unequal n for each group, the output basically provides the group means and > the LD1 value. There is no automatic output of the cutoff (decision > boundary) value used to classify values of the response variable into the > different groups. I have tried various unsuccessful approaches to extract > this value. It is obvious that in the simple 2 group case the value will be > close to the mean of the 2 group means and that the LD1 value is involved > (perhaps grand mean * LD1?). I am probably missing (misunderstanding?) the > obvious and would appreciate being educated in this matter. Thanks. > Regards,BJ > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >-- "Men by nature long to get on to the ultimate truths, and will often be impatient with elementary studies or fight shy of them. If it were possible to reach the ultimate truths without the elementary studies usually prefixed to them, these would not be preparatory studies but superfluous diversions." -- Maimonides (1135-1204) Bert Gunter Genentech Nonclinical Biostatistics [[alternative HTML version deleted]]
On Fri, 23 Sep 2011, B Jessop wrote:> > > >> Hello, I have run a linear discriminant analysis for the simple 2 > group case using the MASS package lda() function. With priors fixed > at 0.5 and unequal n for each group, the output basically provides > the group means and the LD1 value. There is no automatic output of > the cutoff (decision boundary) value used to classify values of the > response variable into the different groups. I have tried various > unsuccessful approaches to extract this value. It is obvious that > in the simple 2 group case the value will be close to the mean of > the 2 group means and that the LD1 value is involved (perhaps grand > mean * LD1?). I am probably missing (misunderstanding?) the obvious > and would appreciate being educated in this matter. Thanks. > Regards,BJYes: 'discrimination' is not 'classification'. However, this and the way to use LDA for classification are covered in the book for which MASS is support software, so please do your homework from that book.> [[alternative HTML version deleted]] > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >-- Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595