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Re: st: base category in margins output
From
Eduardo Nunez <[email protected]>
To
[email protected]
Subject
Re: st: base category in margins output
Date
Wed, 19 Oct 2011 10:30:16 -0400
Richard,
Excelent presentation!
I couldn't, however, get a clue to my question.
The main difference I have with the examples you showed in your
presentation under adjusted predictions is that the default prediction
from a logistic regression is pr; after Cox, is hazard ratio.
Thus, there must be a base group from which the estimate refers to.
Running the univariate Cox, I got the base categories in the results
of the margins as 1 1....1 (as shown below)
Meaning category 1 for urea_2_ca35 & value "0" for LED_sqrt
stcox i.urea_2_ca35##c.LED_sqrt, efron
margins, at(LED_sqrt=(0(3)21) (asobserved) _all) over(urea_2_ca35) post
---------------------------------------------------------------------------------
| Delta-method
| Margin Std. Err. z P>|z| [95%
Conf. Interval]
----------------+----------------------------------------------------------------
_at#urea_2_ca35 |
1 1 | 1 . . . .
.
1 2 | .8365883 .4008474 2.09 0.037 .0509418
1.622235
1 3 | .3564519 .1606048 2.22 0.026 .0416723
.6712315
more output not shown............
When I run the adjusted Cox model, the prior base categories 1 1 now
reports 1.44 (see below)
stcox Iedad__1 sexo dm_i obesidad_i primer_ingreso_i portador_de_dai
pad iam demencia nyha3_4 efLT50##c.sbp_i acxfa##c.fc_i br_i
edemas_tm_i derrame_pleural_i ///
Ina_i__1 Ina_i__2 Iac_u__1 Ibnp___1 Ipcr___1 Icole__1 bbloq_previo_i
bbloq estatina nitratos ieca i.urea_2_ca35##c.LED_sqrt, efron
margins, at(LED_sqrt=(0(3)21) (asobserved) _all) over(urea_2_ca35) post
---------------------------------------------------------------------------------
| Delta-method
| Margin Std. Err. z P>|z| [95%
Conf. Interval]
----------------+----------------------------------------------------------------
_at#urea_2_ca35 |
1 1 | 1.446149 .555207 2.60 0.009 .3579634
2.534335
1 2 | 1.133821 .6742893 1.68 0.093 -.1877618
2.455403
more output not shown............
So, my question is why I am getting in the adjusted model a hazard
ratio of 1.4 instead of 1 for 1 1?
I appreciate your comments on this aparent contradiction.
Best wishes,
Eduardo
On Tue, Oct 18, 2011 at 4:11 PM, Richard Williams
<[email protected]> wrote:
> At 11:53 AM 10/18/2011, Eduardo Nunez wrote:
>>
>> I appreciate any help in understanding this wonderful addition
>> (margins & marginsplot) to Stata 11 & 12.
>
> I don't know if it is a wonderful explanation, but here are the slides for a
> talk I recently gave, which in turn is an expanded version of a talk I gave
> at the Stata Conference this summer.
>
> http://www.nd.edu/~rwilliam/xsoc73994/Margins01.pdf
>
>
> -------------------------------------------
> 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
>
> *
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>
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