We propose a theory of intertemporal choice that is robust to specific assumptions on the discount rate. One class of models requires that one utility stream be chosen over another if and only if its discounted value is higher for all discount factors in a set. Another model focuses on an average discount factor. Yet another model is pessimistic, and evaluates a flow by the lowest available discounted value.

Experimental economists currently lack a convention for how to pay subjects in experiments with multiple tasks. We provide a theoretical framework for analyzing this question. Assuming statewise monotonicity and nothing else, we prove that paying for one randomly chosen problem—the random problem selection mechanism—is essentially the only incentive compatible mechanism. Paying for every period is similarly justified when we assume only a “no complementarities at the top” condition. To help experimenters decide which is appropriate for their particular experiment, we discuss empirical tests of these two assumptions.