R Under development (unstable) (2024-03-08 r86070 ucrt) -- "Unsuffered Consequences"
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> library(survey)
Loading required package: grid
Loading required package: Matrix
Loading required package: survival

Attaching package: 'survey'

The following object is masked from 'package:graphics':

    dotchart

> 
> data(api)
> 
> ## one-stage cluster sample
> dclus1<-svydesign(id=~dnum, weights=~pw, data=apiclus1, fpc=~fpc)
> 
> # svyglm model
> mod <- svyglm(api99 ~ enroll + api.stu, design = dclus1, deff = TRUE)
> 
> #deffs returned from svyglm model - implausibly high
> deff(mod)
(Intercept)      enroll     api.stu 
   1.919945    2.500983    2.686102 
> #> (Intercept)      enroll     api.stu 
> #>    351.3500    457.6799    491.5567
> 
> # run mod with same data and glm()
> srs_mod <- glm(api99 ~ enroll + api.stu, data = apiclus1)
> 
> # manually calculate deffs
> 
> clust_se <- summary(mod)$coefficients[,2]
> srs_se <- summary(srs_mod)$coefficients[,2]
> 
> deffs <- clust_se^2 / srs_se^2
> stopifnot(all.equal(deffs, deff(mod)))
> 
> 
> proc.time()
   user  system elapsed 
   0.90    0.14    1.04