© Reuters / Jo Yong-Hak

A study of the 100 wealthiest Americans has found that most billionaires resemble the conservative Koch brothers more than the Bill Gates-style philanthropic tycoons, but choose to stay silent and let their wallets do the talking.A piece published by the Guardian, Northwestern University professors Benjamin I. Page, Jason Seawright, and Matthew J. Lacombe deliver the findings of an exhaustive study of "everything that the 100 wealthiest US billionaires have said or done, over a 10-year period, concerning several major issues of public policy."The study found that while there are certainly a few prominent and outspoken liberals among the bunch, the so-called philanthropic billionaires like Warren Buffett and Bill Gates are actually more of an anomaly among their super-rich peers.In fact, the study's authors say thatThe difference between these billionaires and the outspoken super-liberal billionaires is that they choose to stay "almost entirely silent"about their opinions, despite having ample opportunity and access to media. But just because we don't hear much from them publicly, doesn't mean they're happy to sit back and see what happens. Instead, they practice what the authors call "stealth politics" - using their vast wealth to wield political influence behind the scenes.One example, the authors say of this public silence vs. private action is on the issue of social security. Most of the billionaires examined in the study have made "substantial financial contributions" to conservative Republicans and officials who are in favor of cutting social security benefits - yet, over a ten-year study period, 97 percent of them said absolutely nothing publicly about social security policy. In other words,In another example, the authors note that while prominent (and atypical) liberal billionaires like Buffett and Gates have spoken publicly in favor of the estate tax, not a single billionaire - liberal or conservative - had taken any action to actually support the tax.The findings, the authors say, help illuminate how the Koch brothers' conservative political network became so powerful. The brothers have had a "fertile field of less-well-known conservative billionaires to cultivate for hundreds of millions of dollars in secret, unreported contributions," they write - a banding together which has produced a "political juggernaut".