Efficient Gain and Loss Amortization and Optimal Funding in Pension Plans

The authors consider efficient methods of amortizing actuarial gains and losses in defined-benefit pension plans. In the context of a simple model where asset gains and losses emerge as a consequence of random (independent and identically distributed) rates of investment return, it has been shown that direct amortization of such gains and losses leads to more variable funding levels and contribution rates, compared with an indirect and proportional form of amortization that “spreads” the gains and losses. Stochastic simulations are performed and they indicate that spreading remains more efficient than amortization with simple AR(1) and MA(1) rates of return. Similar results are obtained when a more comprehensive actuarial stochastic investment model (which includes economic wage inflation) is simulated. Proportional spreading is rationalized as the contribution control that optimizes mean square deviations in the contributions and fund levels when the funding process is Markovian and the fund is invested in two assets (a random risky and a risk-free asset). Efficient spreading and amortization periods are suggested for the United States, the United Kingdom, and Canada.