Determining optimal pool size of a temporary call-in work force

This paper is one in a series that introduces concepts of JUST-IN-TIME-PERSONNEL. Management of worker job time and assignment are in many ways analogous to inventory management. Idle workers represent unutilized, ‘inventoried’ personnel, imposing potentially large costs on management. But a lack of workers when needed may force the use of otherwise unnecessary overtime or other emergency procedures, creating excessive costs analogous to costs of stockout in traditional inventory systems. A system having JUST-IN-TIME-PERSONNEL attempts to meet all demands for personnel at minimum cost by sharply reducing both excess worker inventory with its concomitant ‘paid lost time’ and underage of worker inventory with its associated costs of stockout. The model in this paper focuses on one important component of a JUST-IN-TIME or ‘JIT’ PERSONNEL system: response to day-to-day fluctuations in workload, worker outages due to sick leave, personal constraints or other unscheduled events. To maximize utilization of the JIT concept, the authors assume there exists a pool of call-in personnel who can be called on the day that they are needed. Each such call-in ‘temp’ is guaranteed a minimum number of offered days per month. A temp is paid each month for the days actually worked plus the differential, if any, between the number of days offered and the number of days guaranteed. Temps, like regular workers, may be unavailable on any given day due to illness, etc. The analysis leads to an exact probabilistic model that can be solved to find the optimal pool size of temps. Numerical results are included.