This data set has been originally published in:
The data arose from a clinical trial of 59 epileptics who were randomized to receive either the anti-epileptic drug progabide or a placebo, as an adjuvant to standard chemotherapy. The hope was that progabide would help to reduce the number of seizures experienced by patients. Patients attended four successive post-randomisation clinic visits, where the number of seizures that occurred over the previous 2 weeks was reported. At baseline, information on the age of the patient and the 8-week pre-randomisation seizure count was recorded.
Below is an extract of the data set:
The columns have the following meaning:
- treatment: factor with levels placebo progabide indicating whether the anti-epilepsy drug Progabide has been applied or not. It is a categorical covariate (CAT).
- base: number of epileptic attacks recorded during 8 week period prior to randomization. It is a continuous covariate (COV).
- age: age of the patients.It is a continuous covariate (COV).
- seizure_rate: number of epilepsy attacks patients have during the follow-up period. It is the measurement (Y).
- period: measurement period. It is the time (TIME).
- subject: patient identification number. It is the identifier (ID).
Several points can be noticed:
- There are several seizure counts for each individual, thus the time allows to define to which period it is related.
- ID and TIME column are mandatory. Thus, if there is only one count measurement by individual, an additional column with TIME should be added (full of 0 for example).
- The covariates columns (treatment, base and age) are filled with the same value for each individual. Covariates must be constant within subjects (or subject-occasions when occasions are defined).