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st: RE: Classifying Subjects

From   "Nick Cox" <>
To   <>
Subject   st: RE: Classifying Subjects
Date   Tue, 18 Oct 2005 18:08:33 +0100

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. 


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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