About seven years ago, University of Chicago economists Kerwin Kofi Charles and Erik Hurst were researching the “wealth gap” between black and white Americans when they noticed something striking. African Americans not only had less wealth than whites with similar incomes, they also had significantly more of their assets tied up in cars. The statistic fit a stereotype reinforced by countless bling-filled hip-hop videos: that African Americans spend a lot on cars, clothes, and jewelry—highly visible goods that tell the world the owner has money. But do they really? And, if so, why? The two economists, along with Nikolai Roussanov...