Want to become a billionaire? Up your chances by dropping out of college, working at Goldman Sachs or joining Skull & Bones.

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

We get these questions a lot, and decided it was time to go beyond the broad answers of smarts, ambition and luck by sorting through our database of wealthy individuals in search of bona fide trends. We analyzed everything from the billionaires' parents' professions to where they went to school, their track records in the early stages of their careers and other experiences that may have put them on the path to extreme wealth.

Our 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.

First, a significant percentage of billionaires had parents with a high aptitude for math. The ability to crunch numbers is crucial to becoming a billionaire, and mathematical prowess is hereditary. Some of the most common professions among the parents of American billionaires (for whom we could find the information) were engineer, accountant and small-business owner.

Consistent with the rest of the population, more American billionaires were born in the fall than in any other season. However, relatively few billionaires were born in December, traditionally the month with the eighth highest birth rate. This anomaly holds true among billionaires in the U.S. and abroad.

More than 20% of the 292 of the self-made American billionaires on the most recent list of the World's Billionaires have either never started or never completed college. This is especially true of those destined for careers as technology entrepreneurs: Bill Gates, Steve Jobs, Michael Dell, Larry Ellison, and Theodore Waitt.

Billionaires who derive their fortunes from finance make up one of the most highly educated sub-groups: More than 55% of them have graduate degrees. Nearly 90% of those with M.B.A.s obtained their master's degree from one of three Ivy League schools: Harvard, Columbia or U. Penn's Wharton School of Business.

Goldman Sachs has attracted a large share of hungry minds that went on to garner 10-figure fortunes. At least 11 current and recent billionaire financiers worked at Goldman early in their careers, including Edward Lampert, Daniel Och, Tom Steyer and Richard Perry.

Several billionaires suffered a bitter professional setback early in their careers that heightened their fear of failure. Pharmaceutical tycoon R.J. Kirk's first venture was a flop--an experience he regrets but appreciates. "Failure early on is a necessary condition for success, though not a sufficient one," he told Forbes in 2007.

According to a statement read by Phil Falcone during a congressional hearing in November, his botched buyout of a company in Newark in the early 1990s taught him "several valuable lessons that have had a profound impact upon my success as a hedge fund manager."

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. Among those who were inducted: investor Edward Lampert, Blackstone co-founder Steven Schwarzman, and FedEx founder Frederick Smith.

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. Among them: Bill Gates, Steve Jobs, Michael Dell, Larry Ellison, (Oracle) and Theodore Waitt (Gateway).

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. Among those who were inducted: investor Edward Lampert, Blackstone co-founder Steven Schwarzman and FedEx founder Frederick Smith.

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 billionaires Edward Lampert and Daniel Och, as well as former billionaires Tom Steyer and Richard Perry.

Click here for the full list of billionaire clusters.