The National Transportation Safety Administration performs car crash
experiments.  Twenty new cars, five in each of four size categories, were 
crashed into a fixed barrier ar 35 miles per hour.  Various measurements 
were made on the crash test dummies in the driver's seats.    

The variables in the dataset are:
   size:  SC (subcompact), C (compact), M (midsize), FS (full size)
   head:  head injury score
   chest: chest deceleration in grams
   femur: left femur load in pounds