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| From | Steven Samuels <sjsamuels@gmail.com> |
| To | statalist@hsphsun2.harvard.edu |
| Subject | Re: st: ratio of 2 different surveys estimates? svyset , suest , fpc , nlcom |
| Date | Thu, 20 Jan 2011 09:00:43 -0500 |
"Is this statistically correct..?" Yes Steve sjsamuels@gmail.com On Jan 20, 2011, at 4:03 AM, Roman Kasal wrote: ok, I understand that, I already did this once, but is this statistically correct adjusting=combine FPCs of two different surveys? What if the FPCs are really very different (this is not mentioned case)? -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Steven Samuels Sent: Wednesday, January 19, 2011 9:08 PM To: statalist@hsphsun2.harvard.edu Subject: Re: st: ratio of 2 different surveys estimates? svyset , suest , fpc , nlcom Another way of putting this: When you combine independent surveys, you must create a new stratum variable in which the individual original strata in each survey appear. You would do this in your data, for example by: **************************** egen stratum =group(year stk) ***************************** If there were 10 strata in 2006 and 10 in 2007, the new stratum variable should have 20 levels. Then a single -svyset- statement will allow joint analysis of the two surveys, as in my example. Steve sjsamuels@gmail.com On Jan 18, 2011, at 8:52 PM, Steven Samuels wrote: 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] *********************************************** Steve Steven J. Samuels sjsamuels@gmail.com 18 Cantine's Island Saugerties NY 12477 USA 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 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/