- 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=

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DO NOT SEND Subscribe/Unsubscribe requests to the list! - Dear palapa:

No, you don't. A discriminant function is obtained

as a linear combination of the variables like S=aX+bY+c

and you are supposed to choose a critical value, say G, to

discriminate between the groups depending on whether

S>G or S<G.

Using standardized variables will change only the constant c.

I hope this brief note will help you.

Sincerely yours

Tsuyoshi

> 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 ?"

>

> ==

>

>

>

>

> --

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Tsuyoshi Nakamura

E-mail: nakamura-t@...-u.ac.jp

Fax: 81-95-8431782, Phone: 81-95-8436374

Professor of Biostatistics and Mathematics

Faculty of Environmental Studies

Nagasaki University, Nagasaki 852, JAPAN

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DO NOT SEND Subscribe/Unsubscribe requests to the list! - On Sat, 20 Jun 1998, Palapa wrote:

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

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

> 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=

>

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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DO NOT SEND Subscribe/Unsubscribe requests to the list! - Hi,

I've run a discriminant analysis using SPSSx and have calculated the

discriminant scores. How do I calculate the probability that a case with a

discriminant score of D belongs to a particular group. SPSSx will do the

calculation for me but I would prefer to be able to do it myself.

An old SPSSx Advanced Statistics Guide talks about using Bayes' Rule and

asks the reader to refer to Tatsuoka (1971). The applications Guide for

SPSS version 8.0 suggests computing the Mahalanobis distance. Either way

the calculations are not completed in the text leaving me to find my own

way.

Regards

Adrian Gilbert

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