The first series, the debt-service ratio, measures the required payments on mortgage and consumer debt as a share of after-tax personal income. The second series, the financial-obligations ratio, is a broader version of the debt-service ratio that includes required household payments on rent, auto leases, homeowners insurance, and property taxes. Both ratios rose during the 1990s, and both reached a peak in late 2001.
Rather than requiring higher risk premia from increasingly leveraged borrowers, investors continue to provide financing at declining spreads, fearful of missing out on the returns of those who preceded them.