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,BJ
Yes: '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.
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--
Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
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