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Webster 1913 Edition

Noun.

The quality or state of being representative.

Dr. Burnet observes, that every thought is attended with consciousness and

representativeness

Spectator.

Noun.

The state or quality of being representative.

Dr. Burnet observes that every thought is attended with consciousness and representativeness.

representativeness ‎(uncountable)

The state or quality of being accurately representative of something.
- 2001, Sydney I. Landau, Dictionaries: The Art and Craft of Lexicography, Cambridge University Press (ISBN 0-521-78512-X), page 331,
  One should not compromise on the essential standard of representativeness of the corpus as a whole. A corpus is only good if it can be reasonably trusted to represent the way language is used by those people whose usage one is interested in describing.