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

Thomas Lumley t.lumley at auckland.ac.nz
Wed Dec 7 23:37:36 CET 2016

```No, you can't (at the moment), though it shouldn't be too hard to extend.

I can't run your example, though. I get:

-thomas

Thomas Lumley
Professor of Biostatistics
University of Auckland
________________________________
From: Chris Webb <iknowchris at gmail.com>
Sent: Thursday, December 8, 2016 11:03 AM
To: r-help at r-project.org; Thomas Lumley
Subject: Can you get the DEFT from svyratio?

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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