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Error in SAS documentation of syntax for shared estimate statement

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Occasional Contributor
Posts: 15

Error in SAS documentation of syntax for shared estimate statement

Has anyone ever noticed that there is an obvious error in the documentation for 9.22 on the page with the title, "Positional and Nonpositional Syntax for Coefficients in Linear Functions?"

Actually, I think there are two errors on the page, but I am less certain about the second one.

The documentation asserts that if factor A has three levels and factor B has two levels, then these two procedure calls are equivalent:

proc logistic;

  class a b;

  model y= a b a*b;

  estimate 'B at A2' b 1 -1 a*b 0 0 1 -1;

run;

proc logistic;

  class b a;

  model y=a b a*b;

  estimate 'B at A2' b 1 -1 a*b 0 1 0 0 -1;

run;

This cannot be correct since there are 4 numbers after a*b in the first example but 5 in the second.  I suspect that one of the 0's needs to be removed.  Confirmation?

The second suspicious thing on the page is that the "nonpositional" syntax changes depending on the position of a and b on the class statement.  In what sense would such a syntax be nonpositional?

I think that in both instances, the correct nonpositional syntax is

  estimate 'B at A2' b 1 -1 a*b [1 2 1] [-1 2 2];

Confirmation?

Occasional Contributor
Posts: 15

Re: Error in SAS documentation of syntax for shared estimate statement

Well, I just tested the code.  Should have done that first.  It does work.  So I guess my questions are:

1) Why in the positional syntax are 5 values needed if B is listed first and just 4 if A is listed first?

2) Why does the nonpositional syntax depend on position?

Super User
Posts: 19,822

Re: Error in SAS documentation of syntax for shared estimate statement

What version of SAS are you on?

Occasional Contributor
Posts: 15

Re: Error in SAS documentation of syntax for shared estimate statement

9.3 TS Level 1M1

Occasional Contributor
Posts: 15

Re: Error in SAS documentation of syntax for shared estimate statement

I figured out the first question.  With the positional syntax, there should be 6 coefficients, but SAS assumes that if you name less than 6 then however many at the end are missing, they are all put =0.  Would be really nice if the documentation of this was improved.

So

0 0 1 -1

is the same as

0 0 1 -1 0 0

and

0 1 0 0 -1

is the same as

0 1 0 0 -1 0

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