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RE: Re:st: xtpcse - "no time periods are common to all panels"

 From Nick Cox To "'statalist@hsphsun2.harvard.edu'" Subject RE: Re:st: xtpcse - "no time periods are common to all panels" Date Fri, 18 Nov 2011 13:12:51 +0000

```First, -egen, total()- can work with an expression, so that

egen howmany = total(1), by(year)

would work and a new variable -iota- is not needed.

Second, that in turn is another way of doing

bysort year : gen howmany = _N

Nick
n.j.cox@durham.ac.uk

Christopher Baum

g iota = 1
egen howmany = total(iota), by(year)
tab year howmany
drop if howmany < (number of years)  where number of years refers to the entire dataset's range
tab year howmany

On Nov 18, 2011, at 2:33 AM,Wayne wrote:

> Thanks to Kit, Gordon, and Nick for their helpful answers to my question
> about -xtpcse-.  I had assumed that all of the panels included at least
> some common years, but that was not the case.  There may be easier ways
> to check this, but here is how I did it:
>
> * how many panels are present in each year?
> tabstat year, by(year) stat(N)
> xtset panel_id year
> * what is the pattern of missing years?
> xtdescribe
> by panel_id: gen yrs=_N
> tab yrs
> sort yrs panel_id year
> * visually checking the sorted data, it was easy to see that countries
> with fewer than 12 years of data were the problem
> drop if yrs<12
> drop yrs

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```