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

["Roman Kasal" <kasal@trexima.cz>]

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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