Re: st: Conditional logistic regression: how to

[Marta Garcia-Granero <mgarciagranero@gmail.com>]

Hi Liliana:

Maybe I am missing something, because I'm no Stata expert.

As a former SPSS user, a program that did not have a specific command 
for conditional logistic, I used the well known trick of using survival 
analysis (Cox) instead. Since Stata has -clogit-, I don't think you need 
to declare survival data before running it.

See this simple example (maybe too simple) where -clogit- and -stcox- 
outputs are exactly the same.

* Sample data from www.hrc.es/bioest/Reglog_9.html (coding for hepat had 
to be reversed!!) *
input hepat alcoh drug stratum
1 15 1  1
0 10 0  1
0  0 0  1
1 70 1  2
0 20 0  2
0 30 0  2
1 40 1  3
0 40 0  3
0  0 0  3
1 10 0  4
0 20 1  4
0 50 0  4
1 30 1  5
0 10 0  5
0 20 0  5
1 80 0  6
0 20 0  6
0 30 0  6
1 50 1  7
0 35 0  7
0 10 0  7
1 60 1  8
0  5 0  8
0 10 0  8
1 90 0  9
0 65 0  9
0  5 0  9
1 30 1 10
0 10 0 10
0 40 0 10
end

* Using clogit *
clogit hepat c.alcoh i.drug c.alcoh#i.drug, group(stratum) or

* using Cox *
gen ptime=1+(hepat==0)
stset ptime, failure(hepat==1)
stcox c.alcoh i.drug c.alcoh#i.drug, strata(stratum)

I hope this helps

Marta García-Granero, PhD
Dpt. of Biochemistry and Genetics,
University of Navarra

El 14/11/2013 15:59, liliana escribió:
> Dear statlist users,
>
> I am trying to run a conditional logistic regression. The analysis consists
> of studying the determinants of child mortality. Before running the
> conditional logistic regression I should randomly select pairs from each
> sample, consisting of one death reported during five years preceding the
> survey and one birth that still survived at the survey time. Moreover, I
> have also imputed the missing values of an explanatory variables, which
> means that before the stata command I should insert the mi estimate: option.
>
> What I have done in Stata is
>
> set seed 8021
>
> then I have declared my data to be survival data and then
>
> sttocc, match(mortality), where mortality is a dummy variable assuming value
> 0 if the child died during five years preceding the survey.
>
> Then I go with:
>
> mi estimate: clogit y x1 x2, group(_set)
>
> Stata tells me that
>
> (regular variables _st _d _t _t0 unregistered because not in m=0)
> groups (strata) are not nested within clusters
> an error occurred when mi estimate executed clogit on m=1
> r(459);
>
>
> May you tell me what's wrong with these commands, please?
>
> Thank you very much.
>
> Best,
> Liliana
>
>
>
>
> --
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