"Oxfam’s accounting works like this: your net worth is your assets minus your debts. If your debts equal or exceed your assets, your net worth is negative. By this method, the poorest ten percent on Earth have a combined wealth of minus one trillion dollars. Indeed, the bottom 40% of the world own, in total, nothing (according to this method).
That means if you are debt-free, and have one penny, you are richer than the poorest 40% of the Earth: 2,800,000,000 people.
Debt is a complicated subject, and there’s plenty to be suspicious of in a debt-driven economy. But when you hear that 8 people own more than 50% of the world you probably don’t think, "the 8 richest people’s net worth exceeds that of the fifth decile of people, because on balance, the bottom four deciles have no wealth" — you probably think, "These people are richer than 3.5 billion poor people."