Dear Richard,
Thanks for your clarification. It is very helpful.
Regards
Susanne
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Richard Williams
Sent: Tuesday, February 22, 2005 8:39 AM
To: [email protected]
Subject: Re: st: How to obtain intercepts using svyologit
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.
-------------------------------------------
Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
FAX: (574)288-4373
HOME: (574)289-5227
EMAIL: [email protected]
WWW (personal): http://www.nd.edu/~rwilliam
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