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 <[email protected]> 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
> [email protected]
>
> 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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>
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