A dataframe with 20 observations that shows effect of two soporific
drugs (increase in hours of sleep compared to control) on 10 patients.
| Hours | extra numeric increase in hours of sleep |
| Drug | factor with 2 levels of drug groups (1,2) |
| ID | factor with 10 levels of patient ID (1 to 10) |
| Observation | numeric observation id (1 to 20) |