ricardo,
don't worry about controlling for practice. you've already controlled for
it with the doctor id (i.e., they're perfectly multicollinear). so just
run:
clogit referred, group(doctorid)
and any possible confounding effects of "practice" will be captured &
controlled for by doctorid.
chris
On Mon, 8 Sep 2003, Ricardo Ovaldia wrote:
> Dear all,
>
> I have received only one reply to my post (please see
> my original post below), so either of two things is
> possible: (1) there is not a good answer or (2) my
> question was no clear. So let me ask a slightly
> different question.
>
> Can I simply take the number of referrals at one
> practice and divide by the number of patients seen at
> that practice (referral rate for practice 1) and
> compare it to the rate of the other practice without
> taking in account that some physicians within practice
> may refer more than others? Or, should I compute the
> referral rate for each physician, and then combine
> these rates within practice by weighting them some
> how? If so how can I do this in Stata? what kind of
> weights should I use?
>
> Thank you,
> Ricardo.
>
>
>
> --- Ricardo Ovaldia <[email protected]> wrote:
> > 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 膨logit- to group by
> > doctor痴 ID:
> >
> > . clogit referred practice, group(doctorid)
> >
> > This did not work because the 朴ractice-
> 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,
> > Ricardo.
> >
> >
> > =====
> > Ricardo Ovaldia, MS
> > Statistician
> > Oklahoma City, OK
> >
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