In each of two centres, eligible patients were randomly assigned
to active treatment or placebo. During the treatment, the respiratory
status (categorised poor
or good
) was determined at each
of four, monthly visits. The trial recruited 111 participants
(54 in the active group, 57 in the placebo group) and there were
no missing data for either the responses or the covariates. The
question of interest is to assess whether the treatment is effective
and to estimate its effect.
Note that the data are in long form, i.e, repeated measurments are
stored as additional rows in the data frame.