Research by Singh et al. (1999) as reported in the journal
{\it Clinical Immunology and Immunopathology} is concerned with
immune abnormalities in autistic chilcren.  As part of their
research, they took measurements on the serum concentration of an antigen 
in three samples of children, autistic children,
normal children, and mentally-handicapp0ed children (non-Down's-syndrome).  
All children were 10 years old or younger.  

This dataset contains two variables:

      concentration of the antigen (in units per milliliter of serum)
      group,    coded A for autistic 
                      N for normal
                      M for mentally handicapped