South African Actuarial Journal

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A comparison of probability of ruin and expected discounted utility as objective functions for chosing a post-retirement investment strategy

MBJ Butler, B Hu, D Kloppers


Individuals in defined-contribution retirement funds currently have a number of options as to how to finance their post-retirement spending. The paper considers the ranking of selected annuitisation strategies by the probability of ruin and by expected discounted utility under different scenarios. ‘Ruin’ is defined as occurring when income falls below a given threshold, but does not relate to the extent of that deficit. If there is insufficient money to buy an inflation-linked annuity at retirement, then the minimisation of the probability of ruin tends to result in living annuities with a high equity content. This is because the objective function does not reflect the extent of shortfall of income or the investor’s level of risk aversion. The authors argue that this is a limitation to using the minimisation of the probability of ruin. Expected discounted utility may be more difficult to apply in practice, because of the complexity of explaining the approach to investors and the need to estimate a greater number of parameters explicitly. The authors argue that the use of expected discounted utility is, however, likely to be more representative of most investors’ perception of risk, and illustrate its use by applying an extended discounted utility model that caters for the bequest motive and different reference income levels.

Keywords: Annuities; income drawdown; ruin theory; discounted utility
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