And in the very end - this is exactly what stata lis tries to achieve
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Nick Cox
Sent: 15 May 2006 23:42
To: [email protected]
Subject: st: RE: RE: RE: RE: RE: RE: RE: Excluding Observations
Nothing personal here.
As you say, it is for Raphael Fraser to say what he wants, and he has, I
think, indicated that the code offered solves his problem.
Nick
[email protected]
[email protected]
> Well
> 1) I think the data are about medical treatment (dov == 1), but I
> might be wrong
> 2) I also thought that he is probably intersted in some short-term
> effects, that is why he wants to exclude obs with a visit past 90 days
> after traetment, but I might be wrong again
>
> Don't take my suggestions too personally - it is not meant that way.
> It is probably best the researcher himself decides ( where is he ?)
> what he needs.
Nick Cox
> We are at cross-purposes here. I don't know what you mean by
> "treatment". There is no reference to treatment in the problem.
>
> I believe that I have solved this problem with code that will work.
> Very likely Alex Ogan's solution is equivalent, although
> -drop- is a rather extreme interpretation of "excluding observations".
>
> You should show that my solution is wrong, if you think it is.
>
> Or you could suggest another one, if
> you can think of one that is better or interesting from another point
> of view.
[email protected]
> > I meant the accumulated time after visit with treatment.
> > He does not have that yet. The he will also have obs with dov == 1
> > and 90 days after treatment
>
> Nick Cox
>
> > No. He already has that. You must use the data on transfusions.
>
> [email protected]
>
> > > It looks like to me he has to construct a time variable that
> > > accumulates the number of days since last visit
>
> Nick Cox
>
> > > A visit results in a transfusion whenever t is 1.
> > >
> > > gen ttime = dov if t == 1
> > >
> > > This results in missings whenever t is 0.
> > > Hence we fill in missings following the usual cascade principle
> > > documented at http://www.stata.com/support/faqs/data/missing.html
> > >
> > > bysort id (dov): replace ttime = ttime[_n-1] if mi(ttime)
> > >
> > > Here I am assuming that you want each patient treated separately.
> > >
> > > Then the time since the last transfusion is simply
> > >
> > > gen sincettime = dov - ttime
> > >
> > > Then you can exclude whatever you want. You have to work
> > out what to
> > > do with observations before the first transfusion (on record).
> > >
> > > -etime- is superfluous here.
> > >
> > > Nick
> > > [email protected]
> > >
> > > Raphael Fraser
> > >
> > > > I would like to exclude from my data set all observations
> > up to 90
> > > > days AFTER a transfusion (i.e. t = 1). The variable etime
> > > is the time
> > >
> > > > elapse since last visit. Can any one help?
> > > >
> > > > id dov t etime
> > > > 57 26apr1977 0 57
> > > > 57 27apr1977 0 1
> > > > 57 28jun1977 0 62
> > > > 57 27jul1977 0 29
> > > > 57 19aug1977 1 23
> > > > 57 12sep1977 0 24
>
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