The Collaborative International Dictionary of English v.0.48:

nonrepresentative \nonrepresentative\ adj.
   1. Not standing for something else. Opposite of
      representative.

   Syn: unsymbolic.
        [WordNet 1.5]

   2. Not giving a true representation of the characteristics of
      a group; -- of a sample or subgroup of a group; as, the
      weather we had in the summer of 1996 gave a
      nonrepresentative view of our normal weather.

   Syn: biased, unrepresentative.
        [PJC]

WordNet (r) 3.0 (2006):

nonrepresentative
    adj 1: not standing for something else [syn:
           nonrepresentative, unsymbolic] [ant:
           representative]