Another feature of mortgage contracts is the
use of debt and leverage. Default risk increases
with debt relative to a house’s price, or the
loan-to-value (LTV) ratio. The probability of
default is close to zero at LTV ratios below
80 percent, a rationale for why this threshold
is used as a requirement for borrowers to purchase
additional mortgage insurance. Above
80 percent, the probability of default and its
severity are convex in the LTV. Default risk
rises at each stage for LTV ratios above 85 percent,
90 percent, 95 percent and 100 percent. 2
The vast losses during the financial crisis on
mortgages are consequently concentrated in
loans with high LTV ratios, often not made
to low-income borrowers. With mortgage
default not resulting in personal recourse,
there is the additional problem of ruthless
default. Borrowers will default when they have
income and wealth, but their house has fallen
below the value of the mortgage.