[R] Strange result in survey package: svyvar

Corey Sparks corey.sparks at utsa.edu
Wed Mar 10 19:10:13 CET 2010

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

## 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

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)

[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.

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
corey.sparks 'at' utsa.edu

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