November 17, 2005:
Minimizing the Probability of Lifetime Ruin under Borrowing Constraints
Virginia Young (University of Michigan)
4:00pm, KER 317
(Refreshments precede the talk at 3:30 in Kerchof 314)
We determine the optimal investment strategy of
an individual who targets a given rate of consumption and
who seeks to minimize the probability of going bankrupt
before she dies, also known as lifetime ruin. We impose two
types of borrowing constraints. First, we do not allow the
individual to borrow money to invest in the risky asset nor
to sell the risky asset short. However, the latter is not a
real restriction because in the unconstrained case, the
individual does not sell the risky asset short. Second, we
allow the individual to borrow money but only at a rate
that is higher than the rate earned on the riskless asset.
We consider two forms of the consumption function: (1) The
individual consumes at a constant (real) dollar rate, and
(2) the individual consumes a constant proportion of her
wealth. The first is arguably more realistic, but the
second is closely connected with Merton's model of optimal
consumption and investment under power utility. We
demonstrate that connection in this paper, as well as
include a numerical example to illustrate our results.
[Paper in pdf]