Microsoft co-founder Bill Gates, Amazon boss Jeff Bezos, and veteran financier Warren Buffett now have a combined wealth of $248.5bn (190bn) which is more than the net worth of the 160 million poorest US citizens, the Institute for Policy Studies think tank said. In its report, the Billionaire Bonanza, IPS found that America's top 25 wealthiest people now hold [more than] $1 trillion in wealth. "Our wealthiest 400 now have more wealth combined than the bottom 64 per cent of the US population," the report said. The study found that the median American family has a net worth of $80,000 ... while one in five US households have zero or negative net worth, meaning that their debts are equal to or greater than the worth of their cash and possessions. The figure is higher for people of colour - "underwater households" make up over 30 per cent of black households, and 27 per cent of Latino households. Last month, Forbes reported that it was another record year for the wealthiest people in the world's richest nation. The minimum net worth required to make into the top 400 list is now a record $2bn, up almost a fifth from $1.7bn just twelve months ago.