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Re: st: coding question


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: coding question
Date   Mon, 3 Mar 2008 21:37:30 +0000 (GMT)

Looks ok
-- Maarten

--- Ziad El-Khatib <Ziad.El-Khatib@ki.se> wrote:
> You did kindly answer to this query before, i meant to confirm if i
> want to calculate the cumulative value for first 6 visits only, would
> the command be:
> 
>  bys id (visitn) : gen cumulad = ///
>  sum(pillmissed)/sum(pillspres) * 100, if visitn>=1&visitn<=6
>
> On Wed, Jan 30, 2008 at 12:04 AM, Maarten buis
> > --- Ziad El-Khatib <Ziad.El-Khatib@ki.se> wrote:
> >  > Question how to calculate variable representing cumulative value
> >  > 'cumulad'
> >  >
> >  > = [(total n pillmissed per patient at all visits) / (total n
> >  > pillspres at all visits)] * 100
> >
> >  The trick is to combine -bys- with the -sum- function. -bys id
> >  (visitn)- does whatever folows the : for each person separetely
> and the
> >  (visitn) ensures that within each person the cases are ordered by
> >  visitn. The -sum- function gives you the cumulative sum. So
> combining
> >  the two gives you:
> >
> >  *-------------- begin example ------------------
> >  drop _all
> >  input long id visitn pillspres pillmissed
> >
> > 1001  1   30  2
> >  1001  2   20  5
> >  1001  6   50  1
> >  end
> >
> >  bys id (visitn) : gen cumulad = ///
> >     sum(pillmissed)/sum(pillspres) * 100
> >
> >  list
> >  *--------------- end example --------------------
> >  (For more on how to use examples I sent to the Statalist, see
> >  http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html )


-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------


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