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Re: st: ratio of 2 different surveys estimates? svyset , suest , fpc , nlcom

From   Steven Samuels <[email protected]>
To   [email protected]
Subject   Re: st: ratio of 2 different surveys estimates? svyset , suest , fpc , nlcom
Date   Tue, 18 Jan 2011 20:52:43 -0500

I don't understand all your manipulations, Roman, but I think that the error message provides the key: the same stratum numbers appear in both years, but with different fpcs,, depending on the year. Renumber the strata so that this doesn't happen.

webuse income, clear
gen  year = 2006 + (famid>68)

gen stratum = 1 if  famid<=34                    //2006
replace stratum =2 if  inrange(famid,35,68)      //2006
replace stratum =3 if  inrange(famid, 69, 100)   //2007
replace stratum =4 if inrange(famid, 101,135)    //2007

gen fpc = .05*(stratum==1) +.10*(stratum==2) +.12*(stratum==3) +. 15*(stratum==4)

svyset famid, strata(stratum) fpc(fpc)
svy: reg inc if year==2006
estimates store y2006
svy: reg inc if year==2007
estimates store y2007
suest y2006 y2007
matrix list e(V)   //results from different years are independent
nlcom  _b[y2006:_cons]/_b[y2007:_cons]


Steven J. Samuels
[email protected]
18 Cantine's Island
Saugerties NY 12477
Voice: 845-246-0774
Fax:    206-202-4783

On Jan 18, 2011, at 3:03 AM, Roman Kasal wrote:

I have 2 estemates in 2 surveys with two different FPCs (finite
population corrections). I would like to calculate ratio "nlcom
[r6]_cons/[r7]_cons" but:

for year 2006
svyset ico [pw=vahaHMM], strata(stk) fpc(vb1) singleunit(centered)
svy: reg X if year==2006
estimates save r2006

for year 2007
svyset ico [pw=vahaHMM], strata(stk) fpc(vb1) singleunit(centered)
svy: reg Y if year==2007
estimates save r2007

estu use r2006
estimates esample:
est sto r6

estu use r2007
estimates esample:
est sto r7

suest r6 r7

and error:
fpc for all observations within a stratum must be the same
_robust2 failed to compute cross model variance estimate
likely an internal error in suest


1) is any way how to easily handle this correctly in STATA? Because two
different FPCs are correct for 2 years. Within 1 year (2006 or 2007) the
FPCs are well set because "svy: reg X if year==2006" is working.
2) do I have to calculate the ratio manually? Do you know any tools or
info about this?
3) when I know the fpc does not differ much, can I use average FPC for
the both surveys for the ratio (not for averages)?

thank you

Roman Kasal

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