Contrast in Logistic Regression

[Jean Hanson]

Dear Listers,

I would like to make some comparisons of a categorical variable in a logistic regression model using the contrast syntax titled SPECIAL (matrix). The variable has four levels. I want to compare levels 1 & 3, 1 & 4, and 3 & 4. How would I arrange the matrix? I have tried several ways which did not work. In advance, thank you.

 

Jean Hanson

[Anthony Babinec]

You could write the coefficients like this:

 

LOGISTIC REGRESSION VARIABLES y with x

  /categorical=x/contrast(x)=special(1,0,-1,0, 1,0,0,-1, 0,0,1,-1)

  /METHOD=ENTER x.

 

However, Logistic Regression will warn you that the Special contrasts

have a linear dependency and then stop.

 

Think of the coefficients as columns

 

 1   1   0

 0   0   0

-1   0   1

 0  -1  -1

 

The third column is equal to column 2 – column 1, so this is one way

of seeing the dependency. 

 

Tony Babinec

[hidden email]

 

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From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of Jean Hanson
Sent: Tuesday, February 16, 2010 9:15 AM
To: [hidden email]
Subject: Contrast in Logistic Regression

 

Dear Listers,

I would like to make some comparisons of a categorical variable in a logistic regression model using the contrast syntax titled SPECIAL (matrix). The variable has four levels. I want to compare levels 1 & 3, 1 & 4, and 3 & 4. How would I arrange the matrix? I have tried several ways which did not work. In advance, thank you.

 

Jean Hanson

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