Self-made billionaires may be inherently more giving than those who inherited their wealth, new research suggests.

In fact, they're four times more likely than their counterparts to donate half of their wealth to charity, according to research compiled by Tom Coupé, an associate professor at the Kyiv School of Economics in Ukraine.

Earlier this week, Coupé spoke in conversation with NPR's social science correspondent, Shankar Vedantam, to present findings from his 2014 paper, The Charity of the Extremely Wealthy.

Coupé analyzed data from The Giving Pledge, a movement launched by Bill Gates and Warren Buffet in 2010, which encourages billionaires to commit to giving away half of their fortune. Comparing the signatories with data from the 2013 Forbes billionaires list, Coupé concluded that 85 of the pledge's 114 members were self-made, which is about six percent of all billionaires in the world.

He also found that, unsurprisingly, billionaires with more money were more likely to sign, and billionaires whose fortunes come from the tech and telecommunications sector were twice as likely to sign.

While the findings suggest that self-made billionaires are inherently more generous, there are, of course, other possible explanations. Consider that the two creators of the pledge are both self-made billionaires themselves, and thus possibly spend time with other self-made billionaires who were inspired to join. (Coupé insists that he and his team controlled for this factor.)

One explanation for why self-made billionaires are more generous, if this is in fact the case, is that they have better spending habits, Vedantam said. He also suggested that they are more inclined to want their children to become self-made, and so giving away funds to charity means that they would have less.

It is also possible that self-made billionaires tend to be more confident, and so are less nervous to give away their fortunes, assuming they could reasonably make it back up.