Are billionaires born or made?

What are the common attributes among the uber-wealthy? Are there any true secrets of the self-made?

Forbes.com conducted an admittedly unscientific study of the 657 self-made billionaires we counted in February for our list of the World's Billionaires yielded some interesting results.

Parents Had Math-Related Careers

The ability to crunch numbers is normally a key to becoming a billionaire. Often, mathematical prowess is hereditary. Some of the most common professions among the parents of American billionaires for whom we could find that information were engineer, accountant and small-business owner.

September Birthdays

Of the 380 self-made American tycoons who have appeared on the Forbes list of the World's Billionaires in the past three years, 42 were born in September--more than in any other month. Maybe that's because September is the month the Forbes list of the 400 richest Americans is published.

Tech Titans Who Dropped Out of College

Forget everything your guidance counselor told you: You don't have to go to college to be successful. More than 20% of the self-made American moguls on the most recent list of the World's Billionaires never finished college. Many of them made their fortunes in tech. 

Skull and Bones

Several current and former billionaires rounded out their Yale careers as members of Skull and Bones, the secret society portrayed with enigmatic relish by Hollywood in movies like The Skulls and W. 

Goldman Sachs

A stint at investment bank Goldman Sachs is a prime credential for becoming a finance billionaire. Of the 68 self-made American billionaires that derive their fortunes from finance, at least eight cut their teeth in Goldman's investment banking, trading, or asset management divisions. The company's crown jewel: its "risk arbitrage" unit, which launched the careers of several high profile billionaires. 

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Click here for a full list of billionaire clusters.