Ther dataset "caffeine.dat" contains data on 11 people diagnosed
as being dependent on caffeine.  Each subject was barred from coffee,
colas, and other substances containing caffeine.  Instead, they took
capsules containing their usual caffeine intake.  During a different
time period, they took placebo capsules.  The order in which subjects
took caffeine and the placebo was randomized.  The dataset contains data
on two of several tests given to the subjects.  One is the Beck
Depression Inventory, on which higher scores show more symptoms of depression.
The other is the beats per minute the subject achieved when asked
to press a button 200 times as quickly as possible.  We are
interested in whether being deprived of caffeine affects these outcomes.

The dataset contains one record for each subject.  The four variables are:

   depcaf   -- Beck depression score when taking caffeine capsules
   depnocaf -- Beck depression score when taking placebo capsules
   beatcaf  -- beats per minute when taking caffein capsules
   beatnocaf -- beats per minute when taking placebo capsules