Social class in the United States is a controversial issue, having many competing definitions, models, and even disagreements over its very existence. Many Americans believe in a simple three-class model that includes the "rich", the "middle class", and the "poor". More complex models that have been proposed describe as many as a dozen class levels; while still others deny the very existence, in the European sense, of "social class" in American society. Most definitions of class structure group people according to wealth, income, education, type of occupation, and membership in a specific subculture or social network.