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st: RE: RE: RE: RE: RE: RE: Excluding Observations


From   <J.Fischer@lse.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: RE: RE: RE: RE: Excluding Observations
Date   Mon, 15 May 2006 23:28:00 +0100

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.

Justina 

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
Sent: 15 May 2006 23:22
To: statalist@hsphsun2.harvard.edu
Subject: st: RE: RE: RE: RE: RE: Excluding Observations

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.

Nick
n.j.cox@durham.ac.uk 

J.Fischer@lse.ac.uk
 
> 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. 
 
J.Fischer@lse.ac.uk
  
> > 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
> > n.j.cox@durham.ac.uk
> > 
> > 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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