This view complicates the analysis of the earnings test for a number of reasons. First, many studies have pointed out that there might be heterogeneity in discount rates that makes the future return of lost benefits relatively more favorable for some individuals rather than others. For example, the rate at which benefits are returned is better than actuarially fair for those with lower than population-average mortality risk. Discount-rate heterogeneity could stem from such differences in mortality risk, as well as liquidity constraints and differences in the pure rate of time preference