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Almost all research in appointment scheduling has focused on the trade-off between customer waiting times and server idle times. In this paper, we present an observation-based method for estimating the [...]

This paper compares two types of appointment-scheduling policies for single providers: traditional and open-access. Under traditional scheduling, each of a specified number of patients per day is booked well in [...]

Order crossovers occur when replenishment orders arrive in a sequence that is different than the one in which they were placed. Order crossovers require that optimal reorder levels be set [...]

The Philadelphia, Pennsylvania, Hot Weather-Health Watch/ Warning System was initiated in 1995 to alert the city's population to take precautionary actions when hot weather posed risks to health. The number of lives saved and the economic benefit of this system were estimated using data from 1995 to 1998. Excess mortality in people 65 yr of age and older was defined as reported mortality minus mortality predicted by a historical trend line developed over the period of 1964-88. Excess mortality during heat waves was explained using multiple linear regression. Two variables were convincingly associated with mortality: the time of season when a particular heat wave started, and a warning variable indicating whether or not a heat wave warning had been issued. The estimated coefficient of the warning variable was about -2.6, suggesting that when a warning was issued, 2.6 lives were saved, on average, for each warning day and for 3 days after the warning ended. Given the number of warnings issued over the 3-yr period, the system saved an estimated 117 lives. Estimated dollar costs for running the system were small compared with estimates of the value of a life.

Consider the problem facing a doctor (or other service provider) who is setting patient appointment times in the presence of random service times. He or she must balance the patients' waiting times (if the appointments are scheduled too closely together) against the doctor's idle time (if the appointments are spaced too far apart). Although this problem is fairly intractable, this paper uses the structure of the optimal solution as the basis for a simple closed-form heuristic for setting appointment times. Over a wide test bed of problems, this heuristic is shown to perform on average within 2% (and generally within 0.5%) of the optimal policy.

Order crossover occurs whenever replenishment orders do not arrive in the sequence in which they were placed. This paper argues that order crossover is becoming more prevalent and analyzes the [...]

Tractable (Q,R) heuristic models have been developed for controlling finished goods inventory under continuous review when the service level is explicitly constrained. Q represents the order quantity, while R represents the reorder point. Two tractable closed-form heuristics are used, one based on the limiting behavior as the economic order quantity (EOQ) approaches + infinity, and another a power approximation based on a normal distribution for leadtime demand. The first performs better than using the traditional EOQ , while the second provides excellent cost performance. Other heuristics are shown to perform worse, especially when the EOQ is small relative to the standard derivation of leadtime demand.

Last summer, Philadelphia, Pennsylvania, instituted a new Hot Weather-Health Watch/Warning System (PWWS) to alert the city's residents of potentially oppressive weather situations that could negatively affect health. In addition, the system was used by the Philadelphia Department of Public Health for guidance in the implementation of mitigation procedures during dangerous weather. The system is based on a synoptic climatological procedure that identifies 'oppressive' air masses historically associated with increased human mortality. Airmass occurrence can be predicted up to 48 h in advance with use of model output statistics guidance forecast data. The development and statistical basis of the system are discussed, and an analysis of the procedure's ability to forecast weather situations associated with elevated mortality counts is presented. The PWWS, through greater public awareness of excessive heat conditions, may have played an important role in reducing Philadelphia's total heat-related deaths during the summer of 1995.

Using the 'shortest processing time' queue discipline results in long queues being quickly reduced as the short jobs are quickly pushed through the system. We approximate this effect under the 'first-come, first-served' queue discipline by having the service rate increase with the queue length. That is, instead of picking the shortest job, the server instead picks the first job, but then processes it at a higher rate. This new load-dependent queue is compared with the original queue both individually and within open queueing networks., 1. Introduction Although many multistage systems can be modelled as networks of queues, most of the resulting representations are computationally intractable. One exception is the 'BCMP' model, developed by Baskett, [...]

Multiple production runs are needed when demand is rigid and the manufacturing yield is uncertain. The rigid demand regime was applied to a two-machine setup in which there is an intermediate inventory of inspected units. Based on remaining demand and intermediate inventory level, the production policy must specify which machine to run next and the lot size. A policy improvement algorithm was developed to yield an optimal production policy under rigid demand with uncertain yield.

A well-known characteristic of the EOQ model is that for the optimal order quantity, the average holding costs will equal the average ordering costs. This paper extends this result to a broad class of continuous review inventory models, showing that the average annual costs of following the optimal policy for these models can be quickly calculated as the holding cost times the maximum expected inventory level.

When inventory replenishments can arrive in a different sequence than the one in which they were placed, it is important to use the shortfall distribution to set the base-stock level. Because the exact shortfall distribution is quite difficult to compute, heuristics are commonly used in its stead. Bradley and Robinson [Bradley,J. R., L. W. Robinson. 2005. Improved base-stock approximations for independent stochastic lead times with order crossover. Manufacturing Service Oper. Management 7 319-329.] developed an upper bound on the variance of the number of outstanding orders that they used within a normal approximation of the shortfall distribution. In this short note, we tighten their upper bound and use it within a beta approximation of the shortfall distribution to derive a policy whose costs average only 0.05% above that of the optimal. Key words: inventory policies/management; base-stock policies; stochastic lead time; order crossover History. Received: December 1, 2005; accepted: January 19, 2007. Published online in Articles in Advance December 17, 2007., 1. Introduction When the lead time is stochastic and independent over time, replenishment orders may arrive out of sequence. Bradley and Robinson (2005) develop several tractable normal and negative binomial [...]