Bookmark and Share

Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: st: Brant test interpretation with categorical variables


From   Richard Williams <[email protected]>
To   [email protected]
Subject   Re: st: Brant test interpretation with categorical variables
Date   Fri, 18 Mar 2011 09:09:47 -0500

At 06:14 AM 3/18/2011, Massimiliano Volpi wrote:
Dear Statalisters,

I would like to ask for your help in the interpretation of the results from Brant test (SPost, Scott Long). I am using a number of categorical variables that I expand into dummy variables with the command xi. I have tested my model with Brant and it tipically turns out that only one of the dummies within each categorical variable (which in my case represent the importance of motivations: irrelevant, of little importance, important, etc) violates the assumption of parallel lines. So, I would like to ask whether you would suggest to do a LR test to check whether all the dummies within the same categorical variable simultaneously violate the assumption or whether just one "sub-category" (a single dummy value) is enough to consider the hypothesis to be violated (of course the question only makes sense if the LR test does not reject the parallel line assumption for all the dummies in the same category). It is probably more an econometric question than just one about Stata, but I am getting confused.
Thanks.

Keep in mind that several tests are being made. Therefore, the probability of finding one variable that violates the proportional odds assumption is actually much greater than .05. Doing something like a Bonferroni adjustment, or using a more stringent level of significance, e.g. .01, is reasonable and probably even desirable.

If you want to test the dummies as a block, you can do so with gologit2, available from SSC. Something like

gologit2 y dummy1 dummy2 dummy3 x1 x2, pl sto(m1)
gologit2 y dummy1 dummy2 dummy3 x1 x2, npl(dummy1 dummy2 dummy3) sto(m2)
lrtest m1 m2


-------------------------------------------
Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
HOME:   (574)289-5227
EMAIL:  [email protected]
WWW:    http://www.nd.edu/~rwilliam

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/


© Copyright 1996–2018 StataCorp LLC   |   Terms of use   |   Privacy   |   Contact us   |   Site index