Finite time horizon fill rate analysis for multiple customer cases

The item fill rate - defined as the fraction of demand that is immediately satisfied from on-hand stock - is commonly used as a performance measure in service level agreements between customers and suppliers. Under such agreements, the fill rate is measured over a finite horizon (the performance review period) and the supplier faces a financial penalty if an agreed target is not met. The distribution of the item fill rate (fill rate) determines the probability of exceeding the agreed target, it is therefore a point of interest in SLA coordination. The average finite horizon fill rate decreases with an increase in performance review period length. However, the impact of performance review period length on the shape of the fill rate distribution is not well understood. Past studies of finite horizon fill rate only consider a single customer in the supply chain. In this study, we analyze fill rate distributions for a supplier that has multiple customers each with their own service level agreement. We examine the effects of performance review period length, choice of demand fulfillment (service) policy and correlation between customers' demands on both the average fill rate and the probability of achieving the target fill rate. This study provides new insights into service level agreement coordination between suppliers and customers. For instance, the results show that a supplier with multiple customers must take care with choosing a service policy, as rationing will affect the fill rate distribution and hence the realized service level.