The term "self-made" is somewhat subjective in the world of wealth. Sure, there are billionaires who came from true poverty to strike it rich. But plenty of other so-called self-made rich people started out with affluent families and elite, expensive educations.
To try to fill in the gray areas, Forbes has come out with a "self-made score" for its billionaires. It's like a sliding scale of self-madehood. A score of 1 means they inherited everything. A score of 10 means they grew up poor and overcame "significant obstacles."
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So who are the most self-made billionaires? Among those who get a 10 are: Oprah Winfrey; Sheldon Adelson, the casino king who grew up sleeping on the floor of a Dorchester, Massachusetts, tenement house; and Harold Hamm, the fracking tycoon, who grew up in a family of Oklahoma sharecroppers. (The full spectrum of the list, and corresponding billionaires, is listed below.)
Yet Forbes said that wealth in America has become far more meritocratic over time. It said that in 1984, "less than half of those on The Forbes 400 were self-made; today, 69 percent of the 400 created their own fortunes."
Gates has topped the list for 21 straight years. And, in the latest list, five of the top 10 richest Americans have inherited all or a major part of their wealth. David and Charles Koch, listed as the fourth and fifth richest Americans, get a 5 on the self-made scale, so they're half self-made. The Walton heirs, including Christy, Alice and S. Robson Walton, get scores of between 1 and 4.
This adds to the signs that over the past decade the richest billionaires have become more of a fixed club rather than a revolving door of the richest.
Of the current Forbes 400, there were 34 with a top score of 10; 64 with a score of 9; 130 with a score of 8; 37 with a score of 7; and only 10 with a 6. On the inherited side, there were 28 with a score of 1; 24 with a 2 score; 19 with a 3; 20 with a 4; and 34 with a five.
A 2012 analysis by the left-leaning United for a Fair Economy said that 40 percent of today's American billionaires inherited a "sizeable asset from a spouse or family member."
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"The truth is that Americans have never had an equal opportunity to become wealthy," the report said. "Rather than concocting fables about our 'opportunity society,' the editors of Forbes should be examining the birthright privileges enjoyed by many of those on the list."
Here is Forbes' scoring system and billionaire examples for each score.