scd.RdThese data are from Section 12.2 of Levy and Lemeshow. They describe (a possibly apocryphal) study of survival in out-of-hospital cardiac arrest. Two out of five ambulance stations were sampled from each of three emergency service areas.
data(scd)This data frame contains the following columns:
Emergency Service Area (strata)
Ambulance station (PSU)
estimated number of cardiac arrests
number reaching hospital alive
Levy and Lemeshow. "Sampling of Populations" (3rd edition). Wiley.
data(scd)
## survey design objects
scddes<-svydesign(data=scd, prob=~1, id=~ambulance, strata=~ESA,
nest=TRUE, fpc=rep(5,6))
scdnofpc<-svydesign(data=scd, prob=~1, id=~ambulance, strata=~ESA,
nest=TRUE)
# convert to BRR replicate weights
scd2brr <- as.svrepdesign(scdnofpc, type="BRR")
# or to Rao-Wu bootstrap
scd2boot <- as.svrepdesign(scdnofpc, type="subboot")
# use BRR replicate weights from Levy and Lemeshow
repweights<-2*cbind(c(1,0,1,0,1,0), c(1,0,0,1,0,1), c(0,1,1,0,0,1),
c(0,1,0,1,1,0))
scdrep<-svrepdesign(data=scd, type="BRR", repweights=repweights)
#> Warning: No sampling weights provided: equal probability assumed
# ratio estimates
svyratio(~alive, ~arrests, design=scddes)
#> Ratio estimator: svyratio.survey.design2(~alive, ~arrests, design = scddes)
#> Ratios=
#> arrests
#> alive 0.1535064
#> SEs=
#> arrests
#> alive 0.007596705
svyratio(~alive, ~arrests, design=scdnofpc)
#> Ratio estimator: svyratio.survey.design2(~alive, ~arrests, design = scdnofpc)
#> Ratios=
#> arrests
#> alive 0.1535064
#> SEs=
#> arrests
#> alive 0.009807304
svyratio(~alive, ~arrests, design=scd2brr)
#> Ratio estimator: svyratio.svyrep.design(~alive, ~arrests, design = scd2brr)
#> Ratios=
#> arrests
#> alive 0.1535064
#> SEs=
#> [,1]
#> [1,] 0.009418401
svyratio(~alive, ~arrests, design=scd2boot)
#> Ratio estimator: svyratio.svyrep.design(~alive, ~arrests, design = scd2boot)
#> Ratios=
#> arrests
#> alive 0.1535064
#> SEs=
#> [,1]
#> [1,] 0.01004616
svyratio(~alive, ~arrests, design=scdrep)
#> Ratio estimator: svyratio.svyrep.design(~alive, ~arrests, design = scdrep)
#> Ratios=
#> arrests
#> alive 0.1535064
#> SEs=
#> [,1]
#> [1,] 0.009418401
# or a logistic regression
summary(svyglm(cbind(alive,arrests-alive)~1, family=quasibinomial, design=scdnofpc))
#>
#> Call:
#> svyglm(formula = cbind(alive, arrests - alive) ~ 1, design = scdnofpc,
#> family = quasibinomial)
#>
#> Survey design:
#> svydesign(data = scd, prob = ~1, id = ~ambulance, strata = ~ESA,
#> nest = TRUE)
#>
#> Coefficients:
#> Estimate Std. Error t value Pr(>|t|)
#> (Intercept) -1.70736 0.07547 -22.62 0.000189 ***
#> ---
#> Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
#>
#> (Dispersion parameter for quasibinomial family taken to be 5.645324)
#>
#> Number of Fisher Scoring iterations: 4
#>
summary(svyglm(cbind(alive,arrests-alive)~1, family=quasibinomial, design=scdrep))
#>
#> Call:
#> svyglm(formula = cbind(alive, arrests - alive) ~ 1, family = quasibinomial,
#> design = scdrep)
#>
#> Survey design:
#> svrepdesign.default(data = scd, type = "BRR", repweights = repweights)
#>
#> Coefficients:
#> Estimate Std. Error t value Pr(>|t|)
#> (Intercept) -1.7074 0.1241 -13.75 0.000832 ***
#> ---
#> Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
#>
#> (Dispersion parameter for quasibinomial family taken to be 31.63925)
#>
#> Number of Fisher Scoring iterations: 4
#>
# Because no sampling weights are given, can't compute design effects
# without replacement: use deff="replace"
svymean(~alive+arrests, scddes, deff=TRUE)
#> mean SE DEff
#> alive 46.3333 2.7749 Inf
#> arrests 301.8333 19.6694 Inf
svymean(~alive+arrests, scddes, deff="replace")
#> mean SE DEff
#> alive 46.3333 2.7749 0.0791
#> arrests 301.8333 19.6694 0.0400