Maarten and Kevin: it worked! thank you!
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of
> Xiaoheng Zhang
> Sent: Saturday, March 01, 2008 6:08 PM
> To: [email protected]
> 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 <[email protected]> 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 <[email protected]> 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
> >
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> > *
> > * 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/
>
*
* 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/
