Ranking billionaire wealth is a cottage industry

New York

NEVER before have we had so much information about the world's billionaires. We know their average age (63), their marital status (90 per cent are married, 6 per cent divorced), their most common alma mater (Harvard) and even their most common sign under the Chinese zodiac (the snake). We can get daily updates on their net worth and their competitive positions within the wealth rankings.

An entire cottage industry has grown up around probing and publicising billionaire wealth. At least six different companies now compile billionaire lists.