“If poor people knew how rich rich people are, there would be riots in the streets.” Actor and comedian Chris Rock made this astute statement during a 2014 interview with New York magazine, referring to the yawning gap between rich and poor. In so doing, he stumbled upon a key challenge in the study of inequality. What’s the best way to measure it? Most inequality studies have focused on income – measures of which are widely available. However, being rich is not about a single year of earnings but rather about the accumulation of wealth over time. In the past, quantifying that has been tricky. The wealthy would probably prefer we stay in the dark about how rich they are, presumably to avoid the aforementioned riots.