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

From   Nick Cox <>
To   "''" <>
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 


Christopher Baum

What about

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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