text: Kyle Herkenhoff proposed that the increasing availability of this concept partly explains the rise of unemployment duration since the late 1970s, and the contemporaneous skewing of the wealth distribution, since the unemployed can forego unsuitable job offers.
full_question: Kyle Herkenhoff proposed that the increasing availability of this concept partly explains the rise of unemployment duration since the late 1970s, and the contemporaneous skewing of the wealth distribution, since the unemployed can forego unsuitable job offers. Mian and Sufi's research shows that zip codes in which house prices dropped the most during the financial crisis exhibited the largest drop in demand for non-tradeable services thanks to the buildup of this quantity, which titles their book. The most productive agents are also the least patient ones in Kiyotaki and Moore's endogenous business cycle model, which imposes a collateral requirement to limit this quantity. In that model, a negative shock to the market value of collateral provokes insolvency, which brings about a Fisherian deflation driven by this quantity. The accumulation of this quantity is the driving force in Hyman Minsky's financial instability hypothesis. For 10 points, what is this quantity, which goes up the more spending exceeds income?
first_sentence: Kyle Herkenhoff proposed that the increasing availability of this concept partly explains the rise of unemployment duration since the late 1970s, and the contemporaneous skewing of the wealth distribution, since the unemployed can forego unsuitable job offers.
raw_answer: debt [or credit; prompt on "mortgages"; the title of Mian and Sufi's book is House of Debt]