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RE: st: Variable Manipulation


From   "Katarina Sikavica" <k-sikavica@kellogg.northwestern.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Variable Manipulation
Date   Sat, 1 Mar 2008 19:01:27 +0100

Maarten and Kevin: it worked! thank you! 
 
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu 
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of 
> Xiaoheng Zhang
> Sent: Saturday, March 01, 2008 6:08 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: Variable Manipulation
> 
> Before you trying to impute missing data, it worth to read 
> this tutorial on missing data.
> 
> http://www.lshtm.ac.uk/msu/missingdata/start.html
> 
> Kevin
> 
> On 01/03/2008, Maarten buis <maartenbuis@yahoo.co.uk> wrote:
> > bys company (year) : gen droa = roa - roa[_n-1] bys company 
> (year) : 
> > gen rretind = retind / retind[_n-1]
> >
> > if you have missings than this will become twice as bad for 
> these new
> > variables: say you have missing in roa in 2000 than droa will be 
> > missing in 2000 and 2001. So you might want to consider 
> imputing your 
> > data first before you do this, using for instance -ice-, 
> see: -findit 
> > ice-.
> >
> > Hope this helps,
> > Maarten
> >
> > --- Katarina Sikavica <k-sikavica@kellogg.northwestern.edu> wrote:
> >
> > > Dear Statalisters:
> > >
> > > I am working with a panel dataset containing company performance 
> > > data and would like to calculate
> > > a) the annual change in return on assets (varname: ROA) which is 
> > > calculated as e.g. ROA in the year 2000 - ROA in 2001
> > > b) the ratio of return index (varname: RETIND), calculated as e.g.
> > > RETIND in 2000 / RETIND in 1999
> > >
> > > The dataset is a unbalanced panel of company performance data
> > > 1998-2005
> > > and contains, unfortunately, quite some missings in the 
> performance 
> > > variables (!). The missings are coded using "." The data can be 
> > > grouped according to company name, year (varname: YEAR) 
> and a unique 
> > > numeric
> > > identfier(varname: DSCODE) retrieved frot Thomson Anaytics.
> > >
> > > I have spent some time trying to generate the above mentioned 
> > > variables (I have tried playing around with _n and _N) but was, 
> > > unfortunately unable to obtain the correct variable. I 
> have searched 
> > > STATA FAQ and have used the findit command but given that I don't 
> > > even know what the right keyword is I did not find any useful 
> > > information.
> > > I appologize if this procedure has allready been explained 
> > > elsewhere...
> > >
> > > Many thanks for your help,
> > > Best,
> > > Kate
> > >
> > >
> > > *
> > > *   For searches and help try:
> > > *   http://www.stata.com/support/faqs/res/findit.html
> > > *   http://www.stata.com/support/statalist/faq
> > > *   http://www.ats.ucla.edu/stat/stata/
> > >
> >
> >
> > -----------------------------------------
> > 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/
> > -----------------------------------------
> >
> >
> >      ___________________________________________________________
> > Rise to the challenge for Sport Relief with Yahoo! For Good
> >
> > http://uk.promotions.yahoo.com/forgood/
> > *
> > *   For searches and help try:
> > *   http://www.stata.com/support/faqs/res/findit.html
> > *   http://www.stata.com/support/statalist/faq
> > *   http://www.ats.ucla.edu/stat/stata/
> >
> >
> 
> 
> --
> Greetings,
> 
> Xiaoheng Zhang (Kevin)
> *
> *   For searches and help try:
> *   http://www.stata.com/support/faqs/res/findit.html
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
> 


*
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