Turning k on its head: comments on use of an ED50 in delay discounting research.

Delay discounting (DD) describes how the value of a reinforcer decreases as delay to its delivery increases. Relationships between DD and various aspects of drug abuse have been demonstrated reliably. A potential barrier to wider adoption of DD techniques is that results are often expressed in terms that may be too abstract or unfamiliar to a broader audience, particularly when describing or comparing hyperbolic DD functions or values of k. In an effort to potentially make DD results more accessible, the current report explores use of an ED50 value in characterizing DD functions, similar to that used in pharmacology research for characterizing dose-effect functions. The ED50 proposed with regard to DD is the delay that is effective in discounting the subjective value of the delayed reinforcer by 50%. Additionally, a convenient method for calculating ED50 values for DD is discussed.