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01-23-2009 08:41 PM

I was running SAS on a set of 10 observations each given a rating between 1-3, and another variable A, B or C is assigned to each of them.

e.g.

Obs F1 F2

Ob1 A 1

Ob2 A 3

Ob3 B 3

Ob4 C 2

Ob5 C 3

Ob6 B 1

Ob7 A 3

Ob8 B 3

I used the following to obtain Somers'D

"Proc freq data=xxx;

tables F1*F2 / measures;

run;"

But it comes out differently from the Somers'D in the output of the logistic function

Proc logistic data=xxx;

class F1;

model F1=F2 / rsquare stb;

run;

Then I tried "model F2=F1", the Somers'D still doesn't agree with Freq.

Could anyone help me to understand this please?

e.g.

Obs F1 F2

Ob1 A 1

Ob2 A 3

Ob3 B 3

Ob4 C 2

Ob5 C 3

Ob6 B 1

Ob7 A 3

Ob8 B 3

I used the following to obtain Somers'D

"Proc freq data=xxx;

tables F1*F2 / measures;

run;"

But it comes out differently from the Somers'D in the output of the logistic function

Proc logistic data=xxx;

class F1;

model F1=F2 / rsquare stb;

run;

Then I tried "model F2=F1", the Somers'D still doesn't agree with Freq.

Could anyone help me to understand this please?

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01-25-2009 10:25 AM

Based on the documentation, it looks like FREQ applies a correction for ties and LOGISTIC does not. Your example has at least one tie. Try new sample data without ties.

Doc Muhlbaier

Duke

Doc Muhlbaier

Duke