epil
From MASS v7.347
by Brian Ripley
Thall and Vail (1990) give a data set on twoweek seizure counts for 59 epileptics. The number of seizures was recorded for a baseline period of 8 weeks, and then patients were randomly assigned to a treatment group or a control group. Counts were then recorded for four successive twoweek periods. The subject's age is the only covariate.
 Keywords
 datasets
Usage
epil
Format
This data frame has 236 rows and the following 9 columns:
y
 the count for the 2week period.
trt

treatment,
"placebo"
or"progabide"
. base
 the counts in the baseline 8week period.
age
 subject's age, in years.
V4

0/1
indicator variable of period 4. subject
 subject number, 1 to 59.
period
 period, 1 to 4.
lbase
 logcounts for the baseline period, centred to have zero mean.
lage
 logages, centred to have zero mean.
References
Venables, W. N. and Ripley, B. D. (2002) Modern Applied Statistics with S. Fourth Edition. Springer.
Examples
library(MASS)
summary(glm(y ~ lbase*trt + lage + V4, family = poisson,
data = epil), cor = FALSE)
epil2 < epil[epil$period == 1, ]
epil2["period"] < rep(0, 59); epil2["y"] < epil2["base"]
epil["time"] < 1; epil2["time"] < 4
epil2 < rbind(epil, epil2)
epil2$pred < unclass(epil2$trt) * (epil2$period > 0)
epil2$subject < factor(epil2$subject)
epil3 < aggregate(epil2, list(epil2$subject, epil2$period > 0),
function(x) if(is.numeric(x)) sum(x) else x[1])
epil3$pred < factor(epil3$pred,
labels = c("base", "placebo", "drug"))
contrasts(epil3$pred) < structure(contr.sdif(3),
dimnames = list(NULL, c("placebobase", "drugplacebo")))
summary(glm(y ~ pred + factor(subject) + offset(log(time)),
family = poisson, data = epil3), cor = FALSE)
summary(glmmPQL(y ~ lbase*trt + lage + V4,
random = ~ 1  subject,
family = poisson, data = epil))
summary(glmmPQL(y ~ pred, random = ~1  subject,
family = poisson, data = epil3))
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