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Re: st: Conditional logistic needed?

From   Nada Wasi <>
Subject   Re: st: Conditional logistic needed?
Date   Fri, 5 Sep 2003 09:27:12 -0700 (PDT)


I guess you need to interact "practice" with other
variables, say x, which vary within doctorid, i.e.

clogit referred x x*practice, group(doctorid)


Date: Thu, 4 Sep 2003 15:22:09 -0700 (PDT)
From: Ricardo Ovaldia <>
Subject: st: Conditional logistic needed?

Dear all,

We are interested in comparing the referral rates for
two physician practices.   The fist group has 20
physicians and the second group has 22 physicians.
Each physician saw a variable number of similar
patients some saw as few as 4 and others as many as
43. The physician either referred the patient to a
specialist or did not. 

If I compute the referral rate for each physician
group and compare them, I concerned because the
observations are not independent. I suspect that some
doctors are more likely to refer patients than other.
I though that I could use –clogit- to group by
doctor’s ID:

. clogit referred practice, group(doctorid)

This did not work because the –practice- variable does
not vary within doctor ID, so it is dropped from the
model (omitted due to no within-group variance).

Any suggestions will be greatly appreciated.

Thank you,

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