Epileptic seizure counts

Description

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.

Usage

epilepsy

Format

A dataframe of 236 observations containing information on the following 9 variables.

Age

The age of the patients in years

Base

The seizure count at 8-weeks baseline

Trt

Either 0 or 1 indicating if the patient received anti-convulsant therapy

log_Age_c

The logarithm of Age centered around its mean

log_Base4_c

The logarithm of Base divided by 4 (i.e. log(Base/4)) centered around its mean

Trt_c

Trt centered around its mean

visit

The session number from 1 (first visit) to 4 (last visit)

count

The seizure count between two visits

patient

The patient number

obs

The observation number, i.e. a unique identifier for each observation

Source

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.

Examples

## Not run: 
## poisson regression without random effects. 
fit1 <- brm(count ~ log_Age_c + log_Base4_c * Trt_c, 
            data = epilepsy, family = poisson())
summary(fit1) 
plot(fit1)             
    
## poisson regression with random intercepts of patients and visits
## as well as normal priors for fixed effects parameters.    
fit2 <- brm(count ~ log_Age_c + log_Base4_c * Trt_c 
            + (1|patient) + (1|visit), 
            data = epilepsy, family = poisson(), 
            prior = set_prior("normal(0,5)"))
summary(fit2) 
plot(fit2)

## End(Not run)