[R] logistic regression or discriminant analysis ?
feldesmanm at pdx.edu
Thu May 23 19:38:34 CEST 2002
At 06:25 PM 5/23/2002 +0200, Daniel Amorèse wrote:
>Does logistic regression really provide better results than lda or qda ?
>(my purpose is not classification but highlighting of discriminant
You've asked multiple questions about "stepwise quadratic regression" and
now "stepwise logistic regression". You haven't really explained what you
want to do ("highlighting of discriminant variables" isn't very
informative). WHY do you want to use stepwise anything? Are you looking
for the best set of explanatory variables to predict group membership? Are
your data non-normal? Do your groups have heterogeneous covariance
structures? Do you have vastly unequal mixture proportions?
It sounds like you are interested in the function discrim(), which is part
of S-Plus but not R. You've complained about the lack of documentation for
qda() in Venables and Ripley (3rd edition?) and in the R documentation, but
you haven't told us what you were looking for. Neither qda() nor lda() do
"stepwise", and AFAIK, there is no stepwise logistic regression available
in R. You might want multinomial logistic regression (multinom() in bundle
VR), but that isn't stepwise either.
In short, you're not getting much help because the questions you're asking
aren't very well-formed.
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