Patients with serious spinal cord injury often are paralyzed because of the loss of
neural control of their muscles. They face risks of atrophy, reduced motor function,
and muscle loss.  Exercise and drug therapies are common treatments.  beta_2 adrenergic
agonist is a new drug being tested on patients with spinal injuries.  In an experiment
(Signorile et al., 1995,  Archives of Physical Medicine and Rehabilitation),
patients were randomized to three treatments:  drug therapy with 
$\beta_2$ adrenergic agonist, placebo, and exercise therapy.  After going through
the treatment programs, the strength of the wrist extensor
muscles (in kg) was measured on each patient.  

The dataset spinal.dat has the results of the study.  The two variables are:

     group:  B = beta-2 agonist, P = placebo, E = exercise
     strength:  in kg