Representativeness

n. state of being representative

n. quality of serving on behalf of someone else, vicariousness, state of being representative

The representativeness heuristic is a heuristic wherein commonality between objects of similar appearance is assumed. While often very useful in everyday life, it can also result in neglect of relevant base rates and other errors. The representative heuristic was first identified by Amos Tversky and Daniel Kahneman.
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(n.)
The quality or state of being representative.
  

the degree to which a sample of consumers in a marketing research study represents the characteristics of the population as a whole.