I remember my Dad telling me that time preference is the best measure of class. Class isn't based on race, nationality, religion, or money. The single-best determining factor of class is the ability to forego short-term pleasure for the sake of long-term gain. He told me that a sociologist wrote a book outlining this simple fact, but I never caught the name.
Last weekend, I found it: Edward Banfield. He wrote about time preference and class in The Unheavenly City Revisited (1974). I read about it in Hans-Hermann Hoppe's Democracy: The God that Failed, page 5, fn 6: "Banfield identifies time preference as the underlying cause for the persistent distinction between social classes and cultures, in particular between the 'upper class' and the 'lower class.' Whereas members of the former are characterized by future-orientation, self-discipline, and a willingness to forgo present gratification in exchange for a better future, members of the 'lower class' are characterized by their present-orientation and hedonism."