The Dynamics of Household Debt

Changes in debt-income ratios can be attributed to primary borrowing, interest rates, growth, and inflation. In a new working paper, we apply such a decomposition to the evolution of U.S. household debt. This shows that changes in borrowing behavior has played a smaller role in the growth of household leverage than is widely believed. Rather, most of the increase can be explained in terms of “Fisher dynamics” — the mechanical result of higher interest rates and lower inflation after 1980. Bringing leverage back down will similarly require contributions from factors other than reduced borrowing.

It’s a well-known fact that household debt has exploded in recent decades, rising from 50 percent of GDP in 1980 to over 100 percent on the eve of the Great Recession. It’s also well-known that household borrowing has increased sharply over this period. Indeed, for most people — including many economists — these are two ways of saying the same thing. In fact, though, they are quite different claims, and while the first one is certainly true, the second is not.

How can debt have increased if borrowing hasn’t? Though this seems counterintuitive, the answer is simple. We’re not interested in debt per se, but in leverage, defined as the ratio of a sector’s or unit’s debt to its income (or net worth). This ratio can go up because the numerator rises, or because the denominator falls. Household leverage increased sharply, for instance, in 1930 and 1931 (see Figure 1) but people weren’t were consuming more in the Depression; leverage rose because incomes and prices were falling faster than households could pay down debt. Similarly, changes in interest rates can change the debt burden without any shift in household consumption, because a level of spending that would be compatible with a stable debt-income ratio when interest rates are low will lead to a rising ratio when interest rates are higher. Read more.....