[R] Strange result in survey package: svyvar

[Matthew Dowle]

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"Corey Sparks" <corey.sparks at utsa.edu> wrote in message 
news:C7BD3CA5.206A%corey.sparks at utsa.edu...
> Hi R users,
> I'm using the survey package to calculate summary statistics for a large
> health survey (the Demographic and Health Survey for Honduras, 2006), and
> when I try to calculate the variances for several variables, I get 
> negative
> numbers.  I thought it may be my data, so I ran the example on the help
> page:
>
> data(api)
> ## one-stage cluster sample
> dclus1<-svydesign(id=~dnum, weights=~pw, data=apiclus1, fpc=~fpc)
>
> svyvar(~api00+enroll+api.stu+api99, dclus1)
>        variance     SE
> api00    11182.8 1386.4
> api00    11516.3 1412.9
> api.stu  -4547.1 3164.9
> api99    12735.2 1450.1
>
> If I look at the full matrix for the variances (and covariances):
> test<-svyvar(~api00+enroll+api.stu+api99, dclus1)
>
> print(test, covariance=T)
>                variance      SE
> api00:api00      11182.8  1386.4
> enroll:api00     -5492.4  3458.1
> api.stu:api00    -4547.1  3164.9
> api99:api00      11516.3  1412.9
> api00:enroll     -5492.4  3458.1
> enroll:enroll   136424.3 41377.2
> api.stu:enroll  114035.7 34153.9
> api99:enroll     -3922.3  3589.9
> api00:api.stu    -4547.1  3164.9
> enroll:api.stu  114035.7 34153.9
> api.stu:api.stu  96218.9 28413.7
> api99:api.stu    -3060.0  3260.9
> api00:api99      11516.3  1412.9
> enroll:api99     -3922.3  3589.9
> api.stu:api99    -3060.0  3260.9
> api99:api99      12735.2  1450.1
>
>
> I see that the function is actually returning the covariance for the 
> api.stu
> with the api00 variable.
>
> I can get the correct variances if I just take
> diag(test)
>
> But I just was wondering if anyone else was having this problem.  I'm 
> using
> :
>> sessionInfo()
> R version 2.10.1 Patched (2009-12-20 r50794)
> x86_64-apple-darwin9.8.0
>
> locale:
> [1] en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
> other attached packages:
> [1] survey_3.19
>
> loaded via a namespace (and not attached):
> [1] tools_2.10.1
>
> And have the same error on a linux server.
>
> Thanks,
> Corey
> -- 
> Corey Sparks
> Assistant Professor
> Department of Demography and Organization Studies
> University of Texas at San Antonio
> 501 West Durango Blvd
> Monterey Building 2.270C
> San Antonio, TX 78207
> 210-458-3166
> corey.sparks 'at' utsa.edu
> https://rowdyspace.utsa.edu/users/ozd504/www/index.htm
>