1. A method for conducting demand-based trading, comprising the steps of: establishing a plurality of defined states and a plurality of predetermined termination criteria, wherein each of the defined states corresponds to at least one possible outcome of an event of economic significance; accepting, prior to fulfillment of all of the termination criteria, an investment of value units by each of a plurality of traders in at least one of the plurality of defined states, wherein at least one investment of value units designates a range of possible outcomes corresponding to a set of defined states; and allocating a payout to each investment, responsive to the total number of value units invested in the plurality of defined states, the relative number of value units invested in each of the plurality of defined states, and an identification of the defined state that occurred upon the fulfillment of all of the termination criteria; wherein substantially the same payout is allocated to each state of the set of defined states.