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Re: st: Conditional logistic regression: how to


From   Marta Garcia-Granero <[email protected]>
To   [email protected]
Subject   Re: st: Conditional logistic regression: how to
Date   Mon, 18 Nov 2013 10:25:57 +0100

Ah! Now I see.

Shouldn't your final command be:

mi estimate: clogit _case x1 x2, group(_set)

HTH,
Marta

El 18/11/2013 10:11, Liliana Andriano escribió:
Thank you for your reply Marta. The fact is that I need to estimate
the fixed effects logit regressions relying on conditional logits,
also known as the case-control technique (Chamberlain, 1980), so 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. For
this I have realized that the sttocc command in Stata allows you to
convert survival-time data to case-control data, but before running
it, the declaration of survival data is necessary.

Do you know if I randomly select pairs from each sample even though I
am not declaring survival data and then converting survival-time data
to case-control data?

Your help is very appreciated.
Many thanks in advance.

Best,
Liliana



2013/11/18 Marta Garcia-Granero <[email protected]>:
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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