OK.
Have a look at http://www.stata.com/support/faqs/data/dropmiss.html
as it may contain ideas that you can adapt.
The device of reversing time can be useful (in Stata, that is).
Nick
[email protected]
Thomas Erdmann
> Sorry. I didn't mention that I do not have comprehensive data
> on the point
> of time when the companies were delisted / taken off the market.
>
> So basically I have to assume that if the values repeat up to
> present time,
> that the point where the value is repeated the first time and
> afterwards
> does not change anymore is the point of the delisting.
Nick Cox
> I don't understand the match between your problem
> and your solution.
>
> Sounds to me like
>
> replace var1 = . if status == "Delisted"
>
> but I'm quite likely misunderstanding.
Thomas Erdmann
> > I am working with some variables that or "wrong" in the sense
> > that if one
> > share was taken off the market (i.e. the company was
> > dissolved), the last
> > value of the variable is repeated instead of containing
> > missing values.
> >
> > e.g.
> >
> > Status Year Var1
> > Listed 1991 0.9
> > Listed 1992 0.95
> > Listed 1993 0.93
> > Delisted 1994 0.93
> > Delisted 1995 0.93
> > ..
> > Delisted 2006 0.93 (value is always repeated up to
> present time)
> >
> > Whereas years 1994-2006 should contain missing values. I came
> > up with this
> > cleaning process:
> >
> > foreach X of varlist var1 var2 var3 {
> > generate `X'new=`X'
> > replace `X'new=. if `X'==L.`X'
> > replace `X'=`X'new
> > drop `X'new
> > }
> >
> > Which is okay, but also sets the value to missing if one
> > observation for a
> > listed company repeats, so it also deletes observations that
> > would be fine.
> >
> > Any suggestions on how I can only replace the "wrong" values?
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