R: Epileptic seizure counts

epilepsy {brms} | R Documentation

## 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)

[Package brms version 2.6.0 Index]