Breslow and Clayton (1993) analyze data initially provided by Thall and Vail (1990) concerning seizure counts in a randomized trial of anti-convulsant therapy in epilepsy. Covariates are treatment, 8-week baseline seizure counts, and age of the patients in years.
epilepsyA data frame of 236 observations containing information on the following 9 variables.
The age of the patients in years
The seizure count at 8-weeks baseline
Either 0 or 1 indicating
if the patient received anti-convulsant therapy
The patient number
The session number from 1 (first visit)
to 4 (last visit)
The seizure count between two visits
The observation number, that is a unique identifier for each observation
Standardized Age
Standardized Base
Thall, P. F., & Vail, S. C. (1990).
Some covariance models for longitudinal count data with overdispersion.
Biometrics, 46(2), 657-671.
Breslow, N. E., & Clayton, D. G. (1993). Approximate inference in generalized linear mixed models. Journal of the American Statistical Association, 88(421), 9-25.
if (FALSE) {
## poisson regression without random effects.
fit1 <- brm(count ~ zAge + zBase * Trt,
data = epilepsy, family = poisson())
summary(fit1)
plot(fit1)
## poisson regression with varying intercepts of patients
## as well as normal priors for overall effects parameters.
fit2 <- brm(count ~ zAge + zBase * Trt + (1|patient),
data = epilepsy, family = poisson(),
prior = set_prior("normal(0,5)"))
summary(fit2)
plot(fit2)
}