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Re: st: rate ratios from xtlogit using margins - how?

From   <[email protected]>
To   <[email protected]>
Subject   Re: st: rate ratios from xtlogit using margins - how?
Date   Fri, 17 Dec 2010 14:38:28 +0000

This is exactly what I wanted, checked against my hand calculations for rates and rate ratio and all are the same, plus couldn't figure out how to easily produce rate differences with CIs, which the dydx option with predict now solves - so many thanks.


Dr Seyi Soremekun
Department of Epidemiology and Public Health 
London School of Hygiene and Tropical Medicine
London WC1E 7HT

>>> Maarten buis  17/12/10 1:58 PM >>>
--- On Fri, 17/12/10, SeyiLSHTM wrote:
> I am running an xtlogit model (re) to compare stillbirth
> rates in an intervention (=1) and a control group (=0) with
> clustering. Stata outputs the odds ratio, though I'd rather
> convert this to show the adjusted rates, and an adjusted rate
> ratio or a rate difference (with CIs), as this is more
> intuitive when presenting results to mixed audiences.

The easiest way is probably to look at rates assuming that the
random effect is 0, which is exactly the same as your manual
computation. However, I would let -margins- do those 
computations, by specifying the -predict(pu0)- option, see:
-help margins- and -help xtlogit postestimation-. You can 
also quite easily let -margins compute the rate difference
for categorical variables, by using the -dydx()- option. 

*---------------- begin example ----------------
webuse union, clear
xtlogit union age grade i.not_smsa south##c.year
margins south, predict(pu0)
margins, dydx(south) predict(pu0)
*------------------ end example ----------------
(For more on examples I sent to the Statalist see: )
Hope this helps,

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


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