Offered Load Analysis for Staffing

This essay, based on my 2012 MSOM Fellow Lecture, discusses an idea that has been useful for developing effective methods to set staffing levels in service systems: offered load analysis. The main idea is to tackle a hard problem by first seeking an insightful simplification. For capacity planning to meet uncertain exogenous demand, offered load analysis looks at the amount of capacity that would be used if there were no constraints on its availability. This simplification is helpful because the stochastic model becomes much more tractable. Offered load analysis can be especially helpful when the demand is not only uncertain but also time-varying, as in many service systems. Given the distribution of the stochastic offered load, we often can set staffing levels to stabilize performance at target levels, even in face of a strongly time-varying arrival rate, long service times and network structure.