The ins and outs of mortgage debt during the housing boom and bust

From 1999 to 2013, U.S. mortgage debt doubled before contracting sharply. I estimate mortgage inflows and outflows that shed light on the sources of volatility. During the boom, inflows from real estate investors tripled, far outpacing other segments such as first-time homebuyers. During the bust, a collapse in inflows keyed the debt decline, while an expansion of outflows due to defaults played a more minor role. Inflow declines partly reflect a dramatic falloff in first-time homebuying, especially for low credit score individuals. Further analysis helps support the notion that the differential decline by credit score reflects markedly tightened credit supply.