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st: Re: defiing the reference category in multinominal logistic regression


From   "Martin Weiss" <martin.weiss1@gmx.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Re: defiing the reference category in multinominal logistic regression
Date   Sat, 28 Mar 2009 22:35:24 +0100

<>

Dan,

you do not even apply -xi- to your dependent in the lines

***
-char flushot[omit] 2
-xi: svy: mlogit flushot i.adjsmoker i.ageg i.rostsex i.myrace i.my_income i.my_ed i.my_dwell i.placepar , rr
***

You say "flushot", not "i.flushot"! In fact, the first line here has no effect whatsoever on the second line. The base category for -mlogit- is specified as -baseoutcome()-. -xi- has no bearing on it.

The change in the base category observed in your example is entirely due to the default being the most frequent value of your dependent, and the change you enforce in the second example via "b(2)".


HTH
Martin
_______________________
----- Original Message ----- From: "Dan Waldo" <dan_waldo@yahoo.com>
To: <statalist@hsphsun2.harvard.edu>
Sent: Saturday, March 28, 2009 4:13 PM
Subject: st: defiing the reference category in multinominal logistic regression


Hello, all ...

I am running Stata10/SE, and am doing a series of multinomial logistic regressions.

It's clear that Stata uses information from the
char ageg[omit] 3
instruction (for example) when setting up the explanatory variables. But such is not the case for the dependent variable.

Again for example, the variable flushot is dichotemous with values 1,2 referring to yes,no.

-char flushot[omit] 2
-xi: svy: mlogit flushot i.adjsmoker i.ageg i.rostsex i.myrace i.my_income i.my_ed i.my_dwell i.placepar , rr

produces a regression in which (flushot==Yes is the base outcome)

-xi: svy: mlogit flushot i.adjsmoker i.ageg i.rostsex i.myrace i.my_income i.my_ed i.my_dwell i.placepar , rr b(2)

produces a regression in which (flushot==No is the base outcome)

Am I out of luck is hoping that Stata will use the default reference category when the variable is used as a dependent variable?

Dan Waldo



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