Self-made billionaires are more likely to pledge to donate a large portion of their wealth to charities than those who are heirs to family fortunes, according to new research.

Economists at the University of Southampton examined written testaments of wealthy philanthropists who have signed up to The Giving Pledge, a venture which encourages billionaires to donate at least half of their wealth to charitable causes.

It was launched in 2010 by Warren Buffett and Bill and Melinda Gates.

The analysis found that the super-rich who had made their own fortunes were more likely to sign the Giving Pledge and that philanthropy is impact-driven with the donors stating what changes they want to achieve and displaying a "business-like approach".

The research team concluded that in order for fundraisers to maximise their effectiveness they should target people with newly-acquired fortunes and develop a detailed business plan clearly stating the objectives and the means to achieve these.

By May 2014, the Giving Pledge had 127 families from 12 different countries signed up, with the average age of donors being 69.

The oldest pledger is David Rockefeller Sr, aged 99, and the youngest at 30 are co-founders of Facebook Mark Zuckerberg and Dustin Moskovitz.