# [R] Can you get the DEFT from svyratio?

Chris Webb iknowchris at gmail.com
Wed Dec 7 23:56:30 CET 2016

```Whoops. I forgot to add the one line that I included later in the script.
(I extracted the prior code from a longer document). The code should run
now. It uses dplyr although this could have been done with alternative
methods.

How would you extend svyratio to included calculations for DEFT?

library(survey)
library(dplyr)

# Creating the dataset
df_tbl_10_1 <-
data.frame(
center = c(1,1,1,2,2,2,3,3,3,4,4,4,5,5,5),
nurse = c(rep(c(1,2,3),5)),
seen = c(58,44,18,42,63,10,13,18,37,16,32,10,25,23,23),
referred = c(5,6,6,3,19,2,12,6,30,5,14,4,17,9,14)
)
df_tbl_10_2 <- df_tbl_10_1[c(2,3,4,6,10,11),]

library(dplyr)

df_tbl_10_2 <-
df_tbl_10_2 %>%
mutate(M=5,
Nbar=3,
w=2.5)

# Defining the cluster sampling design
svy_tbl_10_2 <-
svydesign(id=~center + nurse,
data=df_tbl_10_2,
fpc= ~M + Nbar)

# Ratio estimates
svyratio(~referred, ~seen, svy_tbl_10_2)
confint(svyratio(~referred, ~seen, svy_tbl_10_2), df=degf(svy_tbl_10_2))

# DEFF
deff(svyratio(~referred, ~seen, svy_tbl_10_2, deff=TRUE))

# DEFT (fails)
sqrt(deff(svyratio(~referred, ~seen, svy_tbl_10_2, deff="replace")))

On Wed, Dec 7, 2016 at 4:03 PM, Chris Webb <iknowchris at gmail.com> wrote:

> To Dr. Lumley or anyone who may know the answer,
>
> I am trying to obtain ratio estimates from Levy and Lemeshow's Sampling of
> Populations 4th ed. page 281. The results in the book are from STATA.
> According to the STATA output, the DEFT is 0.830749
>
> I can recreate all of the results except for DEFT. For svytotal and
> svymean I can use the option deff="replace" to obtain DEFT results (by
> taking the square root), but I get an error when using this option with
> svyratio. The problem can be my poor understanding of how to calculate
> DEFT, but perhaps it's not implemented for svyratio?
>
>
> R code to that fails:
>
> library(survey)
>
> # Creating the dataset
> df_tbl_10_1 <-
>   data.frame(
>     center = c(1,1,1,2,2,2,3,3,3,4,4,4,5,5,5),
>     nurse = c(rep(c(1,2,3),5)),
>     seen = c(58,44,18,42,63,10,13,18,37,16,32,10,25,23,23),
>     referred = c(5,6,6,3,19,2,12,6,30,5,14,4,17,9,14)
>   )
> df_tbl_10_2 <- df_tbl_10_1[c(2,3,4,6,10,11),]
>
> # Defining the cluster sampling design
> svy_tbl_10_2 <-
>   svydesign(id=~center + nurse,
>             data=df_tbl_10_2,
>             fpc= ~M + Nbar)
>
> # Ratio estimates
> svyratio(~referred, ~seen, svy_tbl_10_2)
> confint(svyratio(~referred, ~seen, svy_tbl_10_2), df=degf(svy_tbl_10_2))
>
> # DEFF
> deff(svyratio(~referred, ~seen, svy_tbl_10_2, deff=TRUE))
>
> # DEFT (fails)
> sqrt(deff(svyratio(~referred, ~seen, svy_tbl_10_2, deff="replace")))
>
> Fail message:
> Error in if (deff) deffs <- matrix(ncol = nd, nrow = nn) : argument is not
> interpretable as logical
>
>
> For other individuals, I have included code that will calculate DEFF and
> DEFT for svytotal on page 280, This code doesn't fail.
>
> svytotal(~referred, svy_tbl_10_2)
> confint(svytotal(~referred, svy_tbl_10_2), df=degf(svy_tbl_10_2))
> deff(svytotal(~referred, svy_tbl_10_2, deff=TRUE))
> sqrt(deff(svytotal(~referred, svy_tbl_10_2, deff="replace")))
>
>
>
> To recap: can you get the DEFT from svyratio?
>
> Sincerely,
> Chris Webb
>

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