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Re: st: corr_svy & covariance matrix for survey data


From   Ishtar Govia <ishtargovia@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: corr_svy & covariance matrix for survey data
Date   Fri, 3 Oct 2008 10:19:55 -0500

Thanks Nick. The correlation runs successfully with my data, except for one issue, the values for one combination of variables (thkdish by trethara) are missing. Any ideas what might have caused this hole in the matrix?

. corr_svy lesscurt lessresp poorserv notsmart actfraid thkdisho actbettr callnmes trethara follstor [pweight=wgtcent], strata(stratum) psu(clust) subpop(dgs1sp) obs sig print(10)

Survey Correlation

pweight: wgtcent
Strata: stratum
PSU: clust

Number of observations: 674

| lesscurt lessresp poorserv notsmart actfraid thkdisho actbettr callnmes trethara follstor
------------- + ------------------------------------------------------------------------------------------------------------------------
lesscurt | 1.0000
| 674
|
|
lessresp | 0.8360 1.0000
| 674 674
| 0.0000
|
poorserv | 0.4326 0.4556 1.0000
| 674 674 674
| 0.0003 0.0002
|
notsmart | 0.5480 0.6199 0.4787 1.0000
| 674 674 674 674
| 0.0000 0.0000 0.0000
|
actfraid | 0.4981 0.5632 0.4310 0.5037 1.0000
| 674 674 674 674 674
| 0.0000 0.0000 0.0001 0.0000
|
thkdisho | 0.4426 0.4273 0.4048 0.5294 0.4423 1.0000
| 674 674 674 674 674 674
| 0.0001 0.0010 0.0001 0.0011 0.0182
|
actbettr | 0.5747 0.6057 0.3899 0.6373 0.6112 0.4671 1.0000
| 674 674 674 674 674 674 674
| 0.0000 0.0000 0.0030 0.0000 0.0000 0.0010
|
callnmes | 0.3420 0.3819 0.3722 0.5454 0.3377 0.3830 0.4690 1.0000
| 674 674 674 674 674 674 674 674
| 0.0027 0.0015 0.0000 0.0001 0.0053 0.0243 0.0026
|
trethara | 0.2388 0.3227 0.3974 0.4355 0.4107 0.4221 0.7472 1.0000
| 674 674 674 674 674 674 674 674
| 0.0093 0.0050 0.0001 0.0175 0.0130 0.0112 0.0001
|
follstor | 0.3973 0.4183 0.5286 0.4711 0.4799 0.3877 0.4689 0.4855 0.5464 1.0000
| 674 674 674 674 674 674 674 674 674 674
| 0.0000 0.0000 0.0001 0.0031 0.0000 0.0014 0.0005 0.0029 0.0005
--------------------------------------------------------------------------------------------------------------------------------------
Key: Estimated Correlation
Number of observations
Significance Level


Ishtar Govia
ishtargovia@gmail.com



On Oct 3, 2008, at 8:32 AM, Nick Winter wrote:


Hi,

-lw- is not an option because listwise is the default. So simply do not specify -pw-, and you will get listwise deletion.

-NW

Ishtar Govia wrote:

Thanks, Nick. The background information on the command and the Stata versions was insightful. The recommendations re: getting around the limitations of the syntax for the subpop were very helpful. I created the single variable (cases either in or out of the subpop) and the following code ran successfully.
corr_svy lesscurt lessresp poorserv notsmart actfraid thkdisho actbettr callnmes trethara follstor [pweight=wgtcent], strata(stratum) psu(clust) subpop(dgs1sp) pw obs sig print(10)
I tried to rerun it specifying a listwise correlation but received the following error message:
corr_svy lesscurt lessresp poorserv notsmart actfraid thkdisho actbettr callnmes trethara follstor [pweight =wgtcent], strata(stratum) psu(clust) subpop(dgs1sp) lw obs sig print(10)
option lw not allowed
r(198);
Is there a reason that lw option for -corr_svy- is not allowed? Or is this again something that is specific to the command being a version 7 command? Or is there some other command that is used to generate the listwise correlation using the -corr_svy-?
On Oct 2, 2008, at 1:02 PM, Nick Winter wrote:

Hi,

I wrote -corr_svy-, so here goes.

There are a couple of things going on here: (1) -corr_svy- is a version 7 command, and seems to be having some trouble interacting with the way that Stata 10 stores the survey characteristics as set by -svyset-. (2) -corr_svy- uses the older, more limited syntax for the -subpop()- option.

Issue (2) means that your subpop option must be specified as a single variable name that takes on values 1 or 0 for cases that are in or out of your subpopulation, respectively. If you have a complex condition, you must first generate such a variable.

So, the following *should* work, but does not:

. sysuse auto
. svyset rep78 [pw=weight]
. corr_svy mpg price , subpop(foreign) sig

Survey Correlation

pweight: <none>
Strata: <one>
PSU: <observations>

Number of observations: 22

| mpg price
-------------+------------------------
mpg | 1.0000
|
|
price | -0.6313 1.0000
| 0.0042
--------------------------------------
Key: Estimated Correlation
Significance Level


As indicated in the output, -corr_svy- has ignored the survey characteristics.

However, you can specify the survey characteristics in the - corr_svy- command itself:

. corr_svy mpg price [pw=weight], psu(rep78) subpop(foreign) sig

Survey Correlation

pweight: weight
Strata: <one>
PSU: rep78

Number of observations: 21

| mpg price
-------------+------------------------
mpg | 1.0000
|
|
price | -0.5735 1.0000
| 0.0344
--------------------------------------
Key: Estimated Correlation
Significance Level


This gives you what you wanted.

(-corr_svy- will also set the survey characteristics you specify in a way that subsequent calls to -corr_svy- can see, so you really only need to specify them in the first run.)

What's going on? With version 9 Stata reworked completely the way that survey characteristics are stored, presumably to support the enhancements to the survey capabilities (such as supporting multiple rounds of sampling). -corr_svy- uses the un/non- documented Stata program -svy_get- to retrieve survey characteristics if they are not specified in the command line. Unfortunately this is a Stata 8 command, and cannot "see" the version 9+ survey characteristics.

In the long run I will fix -corr_svy- to deal with the new survey characteristics. In the short run you can simply specify them when you run -corr_svy_, or with a call to the version 8 -svyset-, like this:

. version 8: svyset ....

As a side effect, this means that -corr_svy- cannot deal with the more complex sample specifications allowed with version 9+.

- Nick Winter


Ishtar Govia wrote:

Dear List,
I am using Stata 10/SE 10.1 for Macs. I have two questions. One concerning the --corr_svy-- module and error messages I have been getting, the second concerning how to obtain a covariance matrix for complex survey sample data, within Stata.
I am working with a complex survey sample dataset and am using Stata for some preliminary data analyses (univariate and multivariate checks for normality, efas) before moving to Mplus for SEM modeling. I installed the --corr_svy-- module from within Stata by typing "ssc install corr_svy"
However, in my first attempt below, I got the following error message:
svy, subpop (if race3cat==2 & sex==1 & (riwyes==1 & riwyes <.)): corr_svy lesscurt lessresp poorserv notsmart actfraid thkdisho actbettr callnmes trethara follstor, pw obs sig
corr_svy is not supported by svy with vce(linearized); see help svy estimation for a list of Stata estimation commands that are supported by svy
r(322);
I then attempted to reset the weight and design variables, and run the --corr_svy--, following the example in the "help" for the --corr_svy--, excluding my subpop specification.
. svyset clust [pweight=wgtcentriw], strata (stratum) ||_n
Note: stage 1 is sampled with replacement; all further stages will be ignored
pweight: wgtcentriw
VCE: linearized
Single unit: missing
Strata 1: stratum
SU 1: clust
FPC 1: <zero>
. corr_svy lesscurt lessresp poorserv notsmart actfraid thkdisho actbettr callnmes trethara follstor, pw obs sig
This worked--but it didn't include my subpop specification. I then tried the same thing with my subpop specifcation and it DIDN'T work. Any ideas on how to use the corr_svy module to obtain the correlation matrix, accounting for the weight and design variables and allowing me to restrict my analyses to my subpop of interest?
corr_svy lesscurt lessresp poorserv notsmart actfraid thkdisho actbettr callnmes trethara follstor [pweight=wgtcent], strata(stratum) psu(clust) subpop(if race3cat==2 & sex==1 & (riwyes==1 & riwyes <.)) pw obs sig print(10) star(5)
subpop() does not contain a valid varname
r(198);
. svyset clust [pweight=wgtcentriw], strata (stratum) ||_n
Note: stage 1 is sampled with replacement; all further stages will be ignored
pweight: wgtcentriw
VCE: linearized
Single unit: missing
Strata 1: stratum
SU 1: clust
FPC 1: <zero>
. corr_svy lesscurt lessresp poorserv notsmart actfraid thkdisho actbettr callnmes trethara follstor, pw obs sig
In addition, does anyone know how to use the matrix I am trying to obtain above to obtain a covariance matrix that can be easily transferred to Mplus or LISREL for CFA and SEM analyses?
Thanks for your consideration,
Ishtar Govia
ishtargovia@gmail.com
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--
--------------------------------------------------------------
Nicholas Winter                                 434.924.6994 t
Assistant Professor                             434.924.3359 f
Department of Politics                  nwinter@virginia.edu e
University of Virginia          faculty.virginia.edu/nwinter w
PO Box 400787, 100 Cabell Hall
Charlottesville, VA 22904

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--
--------------------------------------------------------------
Nicholas Winter                                 434.924.6994 t
Assistant Professor                             434.924.3359 f
Department of Politics                  nwinter@virginia.edu e
University of Virginia          faculty.virginia.edu/nwinter w
PO Box 400787, 100 Cabell Hall
Charlottesville, VA 22904

*
*   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/
*
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*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/



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