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Re: st: Obtaining rrr's of margins after mlogit

From   Maarten Buis <[email protected]>
To   [email protected]
Subject   Re: st: Obtaining rrr's of margins after mlogit
Date   Thu, 22 Mar 2012 13:56:35 +0100

On Thu, Mar 22, 2012 at 12:03 PM, John Francis wrote:
> Now, what do I do in order to check how much the effect has changed
> between cohorts, and whether or not said change is significant? How
> does the constant play into this? I think these things would be fairly
> obvious to see if I could use -margins, over()-, but as it is, the
> -mlogit- output is quite confusing to me...

I think what you are looking for what is discussed in

M.L. Buis (forthcoming) "Stata tip 106: With or without reference",
The Stata Journal, 12(1).

With these tricks you can easily get separate relative risk ratios for
each category, which is sometimes easier to understand. To create an
example with -mlogit-:

*------------------------ begin example -------------------------
sysuse nlsw88, clear

gen occ_cat = cond(occupation < 3                 , 1,      ///
              cond(inlist(occupation, 5, 6, 8, 13), 2, 3))  ///
              if occupation < .
label define occ_cat 1 "high"   ///
                     2 "middle" ///
                     3 "lower"
label value occ_cat occ_cat
gen marst = never_married + 2*married
label define marst 1 "divorced/widowed" ///
                   2 "never married"    ///
                   3 "married"
label value marst marst

gen c_grade = grade - 12			
mlogit occ_cat ibn.marst ibn.marst#c.c_grade, rrr nocons
*------------------------- end example --------------------------
(For more on examples I sent to the Statalist see: )

So the relative risks comparing high with lower occupations (in the
panel labeled "high") for divorced/widowed is .54 person with a higher
job for every person with a lower job. Similarly, for never married it
is .38 person with a higher job for every person with a lower job and
for married it is .43 persons with a higher job for every person with
a lower job. All these relative risks (I like to call them odds [*])
refer to persons with high school (12 years of education).

A year increase in education is associated with an increase in the
relative risks by a factor 1.23, 1.44, and 1.29 for divorced/widowed,
never married, and married persons respectively.

Hope this helps,

[*] <>

Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
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