The two envelope problem: an informed choice

Abstract

The host of a game presents two indistinguishable envelopes to an agent. One of the envelopes is randomly selected and allocated to the agent. The agent is informed that the monetary content of one of the envelopes is twice that of the other. The dilemma is under which conditions it would be beneficial to switch the allocated envelope for the complementary one. The objective of his or her envelope-switching strategy is to determine the benefit of switch- ing the allocated envelope and its content for the expected content of the complementary envelope.

The agent, upon revealing the content of the allocated envelope, must consider the events that are likely to have taken place as a result of the host’s activ- ities. The preceding approach is in stark contrast to considering the agent’s reasoning for a particular outcome that seeks to derive a strategy based on the relative contents of the presented envelopes. However, it is the former reasoning that seeks to identify what the initial amounts could have been, as a result of the observed amount, that facilitates the identification of an appropriate switching strategy.

Knowledge of the content and allocation process is essential for the agent to derive a successful switching strategy, as is the distribution function from which the host sampled the initial amount that is assigned to the first enve- lope.

For every play of the game, once the agent is afforded the opportunity of sight­ing the content of the randomly allocated envelope, he or she can determine the expected benefit of switching.