Re: st: How to obtain intercepts using svyologit

[Richard Williams <Richard.A.Williams.5@nd.edu>]

At 03:05 PM 2/21/2005 +0800, YP Choi wrote:
> Dear all,
>
> I am using the survey commands in stata to analyze stratified data. I am
> running some ordinal logistic regressing models and want to know how I can
> obtain the odds ratio of the intercepts?
> Many thanks for your help.
Somebody can correct me if I am wrong, but I don't believe the term "odds 
ratio" is appropriate when referring to the intercept (which is why Stata 
doesn't report it in the column labeled odds ratio; although other programs 
like SPSS will have a column labeled EXP(B) which includes the 
intercept).  The idea of the odds ratio is that you are contrasting the 
odds of 2 otherwise identical cases where one case scores 1 unit higher on 
the X variable in question.  For a constant, this doesn't make any sense, 
since all cases have a score of one on  the constant.

Nonetheless, in some contexts, you might be interested in the exponentiated 
intercept, e.g. in a logistic regression, an intercept of zero would tell 
you that somebody who scored 0 on all the Xs would have exp(0) = 1 odds of 
success, which corresponds to a 50% chance of success.  If the intercept 
was 1, the probability of success for somebody scoring 0 on all the Xs 
would be 73.1%.  If there are no Xs in the model, e.g. you just do -logit 
y- , then the exponentiated intercept gives you the overall odds of success.

In ordinal logistic regression, however, Stata reports cutpoints, not 
intercepts.  Again, maybe somebody can enlighten me here, but I am not sure 
what an exponentiated cutpoint would mean, at least when there is more than 
1 cutpoint. (If there is only 1 cutpoint, it has the same value but 
opposite sign of what you get when you run a logistic regression.)

But, if you really want exponentiated intercepts or cutpoints, there is 
always your calculator, or the -display- command in Stata.




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Richard Williams, Notre Dame Dept of Sociology
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