On Sat, 20 Jun 1998, Palapa wrote:

> If I want to discriminate between two groups ( A and B). Each group has

> two variable X and Y ( those variables has different unit ).Between A

> and B has different mean value of X and Y. If I standardize the

> variables, each group will contain zero mean of variable X and Y. So

> the difference matrix A and B is Zero.

> "Do we have to standardize the variables before applying

> discriminant analysis ?"

>

> =palapa=

>

As far as I know (AFAIK): Malahanobis distance, used in the

classification/discrimination algorithm, take care of standardization.

Moreover, why standardize by group ? If you do such a thing, you can only

guess that the two correlation matrix will differ, else you'll get not

any difference between the two groups, but discriminant analysis won't

help in such case.

Recall that the assumption here is that the two covariance/correlation

matrixes (spelled right ?) are equal, else you should use quadratic

discriminant analysis or, to get better results, regularized discriminant

analysis.

To summarize: don't standardize.

A quite good and free software (MAC and Win95/NT) for Linear Discriminat

Analysis and much more (no cross-validation):

point to

http://pbil.univ-lyon1.fr/
and go to

http://pbil.univ-lyon1.fr/ADE-4/ADE-4.html
hope that help

federico spinazzi

federico@...
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