When you buy gold you become part of not insignificant community who hold over 6,000 million troy ounces. This is the amount of gold that research firms like Thomson Reuters GFMS estimate exists across the globe – around 187,000 tonnes worth $7.13 trillion dollars.

However, since people are unlikely to truthfully answer a telephone survey about how much gold they have (particularly if they store it at home), how do research firms come up with their estimate?