On the operational definition of processing time uncertainty

Abstract

The uncertainty of processing time has been reported to have a significant effect on the performance of dispatch rules. However, one noticeable result was that dispatch rules directly related to processing times were relatively insensitive to the uncertainty of processing time, while one might have previously expected otherwise. Actual processing times were generated in previous studies in such a way that variation of actual processing time increased together with uncertainty levels. As variation and uncertainty presented as one confounded factor in experiments, one question raised here is whether processing time uncertainty really has a substantial effect on the performance of dispatch rules. A two-stage approach used here investigated the current operational definition of processing time uncertainty by previous researchers and concluded that a new operational definition is desirable?one that isolates uncertainty rather than lumping it in with variation.