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RE: st: RE: Classifying Subjects


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: Classifying Subjects
Date   Tue, 18 Oct 2005 18:27:37 +0100

As earlier said, you need to decide how gaps are to be handled!

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

Raphael Fraser
 
> Yes, gaps do exist in the data since some patients did not turn up for
> their yearly test while others may have turn up three times for the
> year.
> 
> > In addition, it seems possible in principle that
> > an individual could be assigned to two or more
> > classes according to different parts of their history.
> 
> This is true. Therefore if a patient is classed as minimal, sustained
> and heavy, the latter is chosen. If another is assigned minimal and
> sustained then sustained is chosen.
> 
> On 10/18/05, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> > Your example indicates that gaps may exist in the data.
> > Subject 31 was not measured in various years e.g. 1987,
> > 1988. Thus if you want classification according to
> > consecutive years you need to specify how missing
> > [meaning, not present in the data] values are to be
> > treated. Do you mean just consecutive tests?
> >
> > In addition, it seems possible in principle that
> > an individual could be assigned to two or more
> > classes according to different parts of their history.
> >
> > So, I am not clear that writing specific code is
> > the best answer to you until these ambiguities are
> > resolved. But if you go
> >
> > . bysort id (dot) : gen t = _n
> > . tsset id t
> >
> > you can look for spells in your data according to
> > your stated criteria. The user-written
> > program -tsspell- from SSC can be then used. It has
> > a fairly detailed help file.
> >
> > Nick
> > n.j.cox@durham.ac.uk
> >
> > Raphael Fraser
> >
> > > I have a longitudinal data set that contains nearly 500 
> patients. All
> > > patients were tested at these times dot (date of test) 
> for the level
> > > of protein in the blood; the result being 0 (no protein) T (trace
> > > amounts of protein), 1, 2, 3 or 4. I would like to classify these
> > > subjects based on the criteria below:
> > >
> > > "Minimal" if protein is T on at least 2 out of 3 
> consecutive years.
> > > "Sustained" if the result is minimal and lasts 3 years or more.
> > > "Heavy" if sustained with protein  2 or greater lasting 3
> > > years or more.
> > >
> > > id            dot       protein
> > > 31    15mar1985       T
> > > 31    14mar1986       0
> > > 31    15mar1989       T
> > > 31    15mar1990       T
> > > 31    15mar1991       T
> > > 31    15mar1993       0
> > > 31    18feb1994        T
> > > 31    07jun1995        0
> > > 31    23aug1996       1
> > > 31    10may1999      T

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