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st: RE: RE: RE: RE: RE: correlation, panel data


From   "Biljana Dlab" <dlab@isb.uzh.ch>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: RE: RE: RE: correlation, panel data
Date   Thu, 14 Oct 2010 15:01:30 +0200

With this code just vector of dots is generated.

When the loop started, I did not get 2., ...


. tsset  gvkey_n  fyear
       panel variable:  gvkey_n (unbalanced)
        time variable:  fyear, 1971 to 2001, but with gaps
                delta:  1 unit

. levelsof gvkey_n, local(levels)
. gen corr=.
(7609 missing values generated)

. qui foreach l of local levels {
. capture corr cf r_d if gvkey_n==`l'
. if _rc == 0 {
. replace corr=r(rho) if gvkey_n==`l'
. }
. }

. browse

Thanks a lot.

Best,
Biljana

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
Sent: 14 October 2010 14:03
To: 'statalist@hsphsun2.harvard.edu'
Subject: st: RE: RE: RE: RE: correlation, panel data

tsset  gvkey_n  fyear
levelsof gvkey_n, local(levels)
gen corr=.
qui foreach l of local levels {
	capture corr cf r_d if gvkey_n==`l'
	if _rc == 0 { 
		replace corr=r(rho) if gvkey_n==`l'
	} 
}

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

Nick Cox

Put -capture corr- rather than -corr-. 

This rather underlines that if some of your panels are very short, then those correlations will be based on very few values, with consequent problems. For example, a correlation based on two distinct y and two distinct x points will necessarily be 1 or -1. A correlation based on no or one point cannot be calculated. 

Biljana Dlab

I tried to adjust the code, and am getting good results for the first two companies, but then it stops.

This is how I did it:

. tsset  gvkey_n  fyear
       panel variable:  gvkey_n (unbalanced)
        time variable:  fyear, 1971 to 2001, but with gaps
                delta:  1 unit

. levelsof gvkey_n, local(levels)

. gen corr=.
(7609 missing values generated)

. qui foreach l of local levels {
. corr cf r_d if gvkey_n==`l'
. replace corr=r(rho) if gvkey_n==`l'
. }
no observations
r(2000);

Nick Cox

One possibility without installing anything is to modify this recipe:

sysuse auto
levelsof rep78, local(levels)
gen corr = .
qui foreach l of local levels {
	corr mpg weight if rep78 == `l'
	replace corr = r(rho) if rep78 == `l'
}


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