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From |
Veronica Galassi <veronicagalassi@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: How to set calibrated weights |

Date |
Thu, 25 Oct 2012 14:33:59 +0100 |

Dear Steve, Many thanks for your email! I have checked and in the first wave the variable w1_hhcluster is the PSU. In fact, by using the statement: "svyset w1_hhcluster[pw= w1_wgt], strata( w1_hhdc)" the PSUs sum up to 400, as expected. pweight: w1_wgt VCE: linearized Single unit: missing Strata 1: w1_hhdc SU 1: w1_hhcluster FPC 1: <zero> #Obs per Unit ---------------------------- Stratum #Units #Obs min mean max -------- -------- -------- -------- -------- -------- 1 7 303 28 43.3 74 2 10 436 27 43.6 58 3 12 445 22 37.1 60 4 7 310 25 44.3 78 5 6 303 37 50.5 56 6 6 318 45 53.0 73 7 7 212 6 30.3 51 8 7 297 24 42.4 53 9 6 289 29 48.2 73 10 8 229 13 28.6 46 12 8 210 14 26.2 45 13 9 348 6 38.7 53 14 6 281 33 46.8 66 15 7 424 46 60.6 74 16 7 226 5 32.3 48 17 6 222 23 37.0 48 18 7 297 8 42.4 67 19 5 176 28 35.2 52 20 6 160 2 26.7 54 21 9 564 28 62.7 85 22 9 397 24 44.1 69 23 8 465 42 58.1 98 24 7 328 12 46.9 69 25 8 360 32 45.0 66 26 7 397 26 56.7 82 27 5 222 34 44.4 55 28 7 365 30 52.1 70 29 9 368 2 40.9 67 30 11 471 5 42.8 57 31 9 324 24 36.0 52 32 8 330 13 41.2 73 33 7 246 17 35.1 47 34 7 223 7 31.9 62 35 6 275 33 45.8 77 36 9 393 5 43.7 83 37 7 256 8 36.6 67 38 8 379 37 47.4 58 39 6 348 37 58.0 75 40 7 167 1 23.9 58 42 8 345 31 43.1 53 43 7 294 32 42.0 54 44 5 250 38 50.0 57 76 9 353 27 39.2 61 81 5 218 21 43.6 55 82 7 227 24 32.4 39 83 7 354 11 50.6 65 84 4 155 25 38.8 51 88 6 187 4 31.2 60 171 10 443 26 44.3 67 275 10 404 7 40.4 64 572 10 525 16 52.5 114 773 9 314 12 34.9 52 774 12 451 16 37.6 55 -------- -------- -------- -------- -------- -------- 53 400 16884 1 42.2 114 Thanks to you I also managed to find the "cluster" variable in the second wave. Since data are spread among 8 datasets, I did not find it before! However, wen running the statement "svyset cluster[pw= w2_wgt], strata( w2_gc_dc )" the PSUs do not sum up to 400 anymore, as you can see below...is there any explanation for that? Does it mean that "cluster" variable is not the PSU for the second wave? It must be otherwise they would not have labelled it "Original wave 1 sample cluster". Survey: Describing stage 1 sampling units pweight: w2_wgt VCE: linearized Single unit: missing Strata 1: w2_gc_dc SU 1: cluster FPC 1: <zero> #Obs per Unit ---------------------------- Stratum #Units #Obs min mean max -------- -------- -------- -------- -------- -------- 1 8 234 3 29.2 53 2 15 469 1 31.3 67 3 14 363 2 25.9 58 4 11 214 1 19.5 56 5 6 280 21 46.7 68 6 8 307 1 38.4 63 7 8 183 2 22.9 46 8 9 315 1 35.0 67 9 11 302 1 27.5 73 10 13 210 1 16.2 39 12 20 204 1 10.2 34 13 15 431 1 28.7 64 14 11 296 1 26.9 64 15 13 425 1 32.7 76 16 8 209 1 26.1 50 17 11 222 1 20.2 46 18 10 265 1 26.5 57 19 7 153 1 21.9 38 20 11 173 1 15.7 55 21 10 638 1 63.8 99 22 16 455 1 28.4 88 23 12 651 1 54.2 121 24 10 443 2 44.3 112 25 12 573 1 47.8 108 26 7 405 11 57.9 102 27 9 206 1 22.9 51 28 11 478 1 43.5 89 29 11 388 1 35.3 73 30 18 511 1 28.4 64 31 24 375 1 15.6 54 32 11 359 1 32.6 87 33 13 328 1 25.2 69 34 15 245 1 16.3 71 35 18 317 1 17.6 82 36 13 440 2 33.8 93 37 23 278 1 12.1 64 38 16 442 1 27.6 76 39 10 376 1 37.6 76 40 18 154 1 8.6 45 42 14 347 1 24.8 62 43 10 400 1 40.0 77 44 8 236 2 29.5 58 76 40 374 1 9.3 75 81 11 237 1 21.5 58 82 9 187 2 20.8 45 83 14 384 1 27.4 72 84 5 205 1 41.0 69 88 33 233 1 7.1 64 171 30 474 1 15.8 67 275 13 403 1 31.0 56 572 31 665 1 21.5 112 773 30 285 1 9.5 39 774 59 505 1 8.6 60 -------- -------- -------- -------- -------- -------- 53 793 18252 1 23.0 121 18285 = #Obs with missing values in the -------- survey characteristics 36537 2012/10/24 Steve Samuels <sjsamuels@gmail.com>: > I looked at the documentation some more; the corresponding variable in > Wave 2 is "cluster". You could have discovered this for yourself by > typing "lookfor cluster", which would identify any variable whose name > or label contained "cluster". > > But I am not sure that this _is_ the PSU, though used in the (incorrect) > published Stata example. According to: Methodology: Report on NIDS Wave > 1 Technical Paper no. 1, page 9, quoted below, "cluster" is the name of > the *second* stage sampling unit, not the *primary* sampling unit. Double > check with your contact. > > > Quote from Methodology Report, page 8 > > 3.2 Sample of dwelling units At the time that the Master Sample was > compiled, 8 non-overlapping samples of dwelling units were > systematically drawn within each PSU. Each of these samples is called a > “cluster” by Stats SA. These clusters were then allocated to the various > household surveys that were conducted by Stats SA between 2004 and 2007. > However, two clusters in each PSU were never used by Stats SA and these were > allocated to NIDS. > > Steve > >> >> >> >> On October 23, Veronica Galassi wrote: >> >> >> As you correctly said, looking at the wave 1 it is possible to >> understand that the PSU variable is "w1_hhcluster". >> However, this variable is missing in wave 2 so I contacted the person >> responsible for the data management of the survey and they should >> provide me with this variable soon! >> >> Many thanks again for your support, dear Steve, and for the passion >> you put on helping people in trouble with Stata! >> >> All the best, >> >> Veronica >> >> >> Veronica: >> >> "Introduction to Wave 1 Data May 2012" >> >> I look through the NIDS web site information for Wave 2 and finally resorted to a Google Search for ' "NIDS >> svyset and got a hit to "Introduction to Wave 1 Data May 2012" at: http://www.nids.uct.ac.za/home/index.php?/Nids-Documentation/documents.html >> >> There is the statement : >> "In Stata the recommended svyset command is svyset [pw= w1_wgt], strata(w1_hhdc) psu( w1_hhcluster)." >> >> This is incorrect syntax. The proper syntax for -svyset- would be > > ************************************************* > svyset w1_hhcluster [pw= w1_wgt], strata(w1_hhdc) > ************************************************ > > Now, you have to find the equivalent w2_ variables. The clue to the PSU is that it takes on 400 unique values. It might be w2_hhcluster, but is could be w2_hhgeo. which you picked out as a cluster variable. > > So the correct statement is likely to be either: > ************************************************* > svyset w2_hhcluster [pw= w2_wgt], strata(w2_hhdc) > svydes > ************************************************ > OR > ************************************************* > svyset w2_hhgeo [pw= w2_wgt], strata(w2_hhdc) > svydes > ************************************************ > > The one with #units = 400 distinct values is correct If both show 400 units, see which one reproduces Table 2 of the "Introduction to Wave 1 Data May 2012". The following code can help do this: > ************************************* > egen t_geo = tag(ww2_hhgeo) > egen t_cluster = tag(ww2_hhcluster) > tab w2_gc_prov if t_geo > tab w2_gc_prov if t_cluster > ************************************* > > So it is up to you to do the detective work and to study about survey design. > Good luck. > > Steve > > > > > > On Oct 21, 2012, at 5:05 AM, Veronica Galassi wrote: > > Dear Steve, > > Thank you very much for your time. > > This is the quote from the document describing the sampling > methodology (Methodology: Report on NiDS Wave 1, page 9). This > technical document and the one explaining how weights have been built > can be found here: > http://www.nids.uct.ac.za/home/index.php?/Nids-Documentation/technical-papers.html. > "A stratified, two-stage cluster design was employed to be included in > the base wave. In the first stage, 400 PSUs where included from Stats > SA's 2003 Master Sample of 3,000 PSUs...A PSU is defined as a > geographical area that consists of at least one Enumeration Area (EA) > or several EAs from the 2001 census...In some cases it has been > necessary to add EAs to the original EA to meet the requirement of a > minimum of 74 households per PSU." > I tried to contact the organisation responsible for the survey asking > for more info regarding the PSU but they did not come back to me. The > reason why I called the clusters "cluster 1" and "cluster 2" is just > to distinguish them from each other. In the above-mentioned document > there is no clear reference to province and geographical type being > cluster 1 and 2. Looking at the variables in the dataset and reading > the documents, I deduced they were the two clusters in question. > > This is what I typed when I tried not to specify the PSU: > "svyset [pw=w2_wgt], strata ( w2_gc_dc)|| w2_hhgeo|| w2_gc_prov" > And this is the error I got back (r198):"invalid use of _n; > observations can only be sampled in the final stage". > > Yes, I tried to set the weights following the statement: "w2_gc_prov > [pw = w2_wgt], strata(w2_gc_dc) || w2_hhgeo" followed by svydes. > This is the output: > > #Obs per Unit > ---------------------------- > Stratum #Units #Obs min mean max > -------- -------- -------- -------- -------- -------- > 1 1* 234 234 234.0 234 > 2 1* 469 469 469.0 469 > 3 1* 363 363 363.0 363 > 4 1* 214 214 214.0 214 > 5 1* 280 280 280.0 280 > 6 1* 307 307 307.0 307 > 7 1* 183 183 183.0 183 > 8 1* 315 315 315.0 315 > 9 1* 302 302 302.0 302 > 10 1* 210 210 210.0 210 > 12 1* 204 204 204.0 204 > 13 1* 431 431 431.0 431 > 14 1* 296 296 296.0 296 > 15 1* 425 425 425.0 425 > 16 1* 209 209 209.0 209 > 17 1* 222 222 222.0 222 > 18 1* 265 265 265.0 265 > 19 1* 153 153 153.0 153 > 20 1* 173 173 173.0 173 > 21 1* 638 638 638.0 638 > 22 1* 455 455 455.0 455 > 23 1* 651 651 651.0 651 > 24 1* 443 443 443.0 443 > 25 1* 573 573 573.0 573 > 26 1* 405 405 405.0 405 > 27 1* 206 206 206.0 206 > 28 1* 478 478 478.0 478 > 29 1* 388 388 388.0 388 > 30 1* 511 511 511.0 511 > 31 1* 375 375 375.0 375 > 32 1* 359 359 359.0 359 > 33 1* 328 328 328.0 328 > 34 1* 245 245 245.0 245 > 35 1* 317 317 317.0 317 > 36 1* 440 440 440.0 440 > 37 1* 278 278 278.0 278 > 38 1* 442 442 442.0 442 > 39 1* 376 376 376.0 376 > 40 1* 154 154 154.0 154 > 42 1* 347 347 347.0 347 > 43 1* 400 400 400.0 400 > 44 1* 236 236 236.0 236 > 76 2 374 124 187.0 250 > 81 2 237 50 118.5 187 > 82 2 187 3 93.5 184 > 83 2 384 73 192.0 311 > 84 2 205 2 102.5 203 > 88 2 233 14 116.5 219 > 171 1* 474 474 474.0 474 > 275 1* 403 403 403.0 403 > 572 1* 665 665 665.0 665 > 773 1* 285 285 285.0 285 > 774 1* 505 505 505.0 505 > -------- -------- -------- -------- -------- -------- > 53 59 18252 2 309.4 665 > > 3703 = #Obs with missing values in the > -------- survey characteristics > 21955 > > > After having set the weights in this way, I tried to conduct some > descriptive statistics by typing:"svy: mean (tot_grem_k) if > tot_grem_k>0 & w2_a_cgprv1!=10" > I got back the mean but the standard errors were missing. In fact, > Stata gave me back the following note:"Note: missing standard error > because of stratum with single sampling unit.",as it is clearly shown > in the table above. > > I hope this clarifies the sampling methodology a bit. > Thank you so much for your precious help, I am learning a lot from > your comments!!! > > Kind regards, > > Veronica > > > > > 2012/10/20 Steve Samuels <sjsamuels@gmail.com>: >>> >>> On Oct 20, 2012, at 5:08 AM, Veronica Galassi wrote: >>> >>> Dear Steve, >>> >>> Thank you very much for your kind reply and the useful references! >>> Your answer actually clarified many other doubts I had. >>> >>> Your intuition that my post-stratified weights are calibrated is >>> correct. Unfortunately, I checked again the documents explaining the >>> sampling methodology and there the PSU is simply defined as a >>> geographic area containing more than 74 dwellings. Therefore I expect >>> the number of PSU to be high (around 3,000) whereas I only have 9 >>> provinces and 4 geographical types in my survey. This implies that >>> none of my cluster variables can be the PSU. >> >> You still haven't persuaded me. I'd have to see the quote from the study >> documents. Or, better, post a link to them if they are online. You'd >> better figure out what role, if any, the cluster variables have in the >> design. Why did you name them "cluster 1" and "cluster 2"? >>> However, if I got your point, it does not really matter which PSU I >>> indicate when conducting descriptive statistics. Is it correct? >> >> No, it is not. It is scientifically irresponsible to publish estimates >> of descriptive statistics without indications of uncertainty (SEs, CIs). >> >>> For >>> this reason, I also tried not to indicate any PSU but Stata gave me >>> back the error: "invalid use of _n; observations can only be sampled >>> in the final stage". >> See FAQ Section 3.3 First stence >> >>> To cut it short, do you still believe I can use the statement "svyset >>> w2_gc_prov [pw = w2_wgt], strata(w2_gc_dc) || w2_hhgeo" you previously >>> indicated to set my calibrated weigths? ( In my case I cannot use the >>> fpc option). >> >> I don't know, because you have not yet correctly described the sampling >> design. As an aside, ave you even tried the statement, which assumed >> that w2_gc_prov is the OSY? When you do, follow it by -svydes-. >> >>> >> 2012/10/20 Steve Samuels <sjsamuels@gmail.com>: >>> Veronica, >>> >>> The PSU variable is not missing. It is the sampling unit at the first >>> stage of sampling and it's one of your cluster variables, probably >>> "cluster 1" (check). Your statement that one must know the PSU variable >>> to use probability weights is also incorrect. One can get proper >>> weighted estimates, though not standard errors, without knowing the PSU. >>> >>> I'm not sure what wrong with your -concat- statement. I would have >>> used "egen combination = group()". For it to have worked, the value of >>> the "post-stratification weight" would have to be the population count >>> for each combination of the three variables. >>> >>> If the "post-stratification" weights are not integers, they are probably >>> "calibration" weights that have already adjusted the probability >>> weights. In that case, further post-stratification are likely to be >>> superfluous. You would then use the "post-stratification weight" in place of >>> the probability weights. All weights should be >>> described in the study documents (though usually not the"codebook"). If >>> they are not, then contact the organization that did the study for >>> details. >>> >>> If sampling was without replacement at one or more stages, >>> you could use the fpc() option for those stages. In practice, >>> it makes a difference only for the first stage. >>> >>> In any case, one guess at a -svyset- statement (assuming the >>> "post-stratification weight" is a "calibration" weight) is: >>> ************************************************************* >>> svyset w2_gc_prov [pw = w2_wgt], strata(w2_gc_dc) || w2_hhgeo >>> ************************************************************** >>> >>> But I could be wrong, depending on how w2_wgt was calculated. >>> >>> Before proceeding, I suggest that you learn more about sampling or take >>> a survey course. I gave some references in: >>> http://www.stata.com/statalist/archive/2012-09/msg01058.html. >>> The Stata survey manual is also a very good resource, though the section on >>> post-stratification is skimpy. >>> >>> Steve >>> >>> >>> On Oct 19, 2012, at 1:57 PM, Veronica Galassi wrote: >>> >>> Dear Statalisters, >>> >>> I am writing you concerning the application of calibrated weights to >>> my dataset for the computation of descriptive statistics only. >>> >>> The dataset I am working on collects information at household and >>> individual level and comes from a stratified, two-stage clustered >>> sample. The followings are the variables I have got: >>> - probability weights: w2_dwgt >>> - strata: w2_gc_dc >>> - cluster 1: w2_gc_prov >>> - cluster 2: w2_hhgeo >>> - post-stratified weights: w2_wgt >>> - age intervals: w2_age_intervals >>> - gender: w2_best_gen >>> - population group: w2_best_race >>> >>> In order to set the probability weights using the command svyset, I >>> need the psu variable. As you may have noticed, this variable is >>> missing and this makes me impossible to set pweights. >>> In addition, from a couple of previous statalist conversations ( see >>> in particular: http://www.ats.ucla.edu/stat/stata/faq/svy_stata_post.htm >>> and http://www.stata.com/statalist/archive/2012-02/msg00584.html), I >>> understood that: >>> - when using calibrated weights I still have to set pweights and >>> specify the original strata and clusters >>> - In order to apply calibrated data I need to know the characteristics >>> on the base of which the sample have been post-stratified ( in my case >>> age intervals, gender and population groups). >>> >>> Therefore, I tried to set my post-stratified weights using the >>> following command: >>> "svyset [pw=w2_dwgt], strata (w2_gc_dc) poststrata (w2_age_intervals >>> w2_best_gen w2_best_race) postweight(w2_wgt)" >>> which did not work because in Stata the poststrata must be mutually >>> exclusive and thus only one variable can be specified. >>> >>> In order to overcome this problem, I tried to generate a variable >>> which is a combination of the three characteristics by using the >>> command >>> "egen combination=concat( w2_age_intervals w2_best_race w2_best_gen), >>> format (float)". >>> However, this command generated a variable containing only missing >>> values and for this reason Stata gave me back the error: >>> "option postweight() requires option poststrata()". >>> The only way to make Stata set the post-calibrated weight was by using >>> the command >>> "svyset, poststrata (combination) postweight(w2_wgt)" with combination >>> being a string variable. However I am scared that this command is not >>> complete. >>> >>> At this point, I would really appreciate any hint on what I am doing >>> wrong and how to proceed to set my post-stratified weights. >>> >>> Many thanks for your help! >>> >>> Kind regards, >>> >>> Veronica Galassi >>> * >>> * For searches and help try: >>> * http://www.stata.com/help.cgi?search >>> * http://www.stata.com/support/faqs/resources/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/faqs/resources/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/faqs/resources/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/faqs/resources/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/faqs/resources/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/faqs/resources/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/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: How to set calibrated weights***From:*Steve Samuels <sjsamuels@gmail.com>

**References**:**st: How to set calibrated weights***From:*Veronica Galassi <veronicagalassi@gmail.com>

**Re: st: How to set calibrated weights***From:*Steve Samuels <sjsamuels@gmail.com>

**Re: st: How to set calibrated weights***From:*Veronica Galassi <veronicagalassi@gmail.com>

**Re: st: How to set calibrated weights***From:*Steve Samuels <sjsamuels@gmail.com>

**Re: st: How to set calibrated weights***From:*Veronica Galassi <veronicagalassi@gmail.com>

**Re: st: How to set calibrated weights***From:*Steve Samuels <sjsamuels@gmail.com>

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