Fair measures of performance: the World Cup of cricket

Luck can play a big part in tournament success, and progress is not necessarily the best measure of performance. A linear model is used to fit least squares ratings to margins of victory in the cricket World Cup. The Duckworth/Lewis rain interruption rules are used to project a winning second innings score and create a margin of victory in runs, equivalent to that used when the team batting first wins. Results show that, while the better teams progressed through the first round of the competition, some injustices occurred in the Super-Six round. This appears to be due to the double counting of selected matches. Ordering teams by average margin of victory gives similar results to the more complicated linear model, and its use as a tie breaker is suggested. Publication of the margin of victory as estimated by the Duckworth/Lewis method for second innings victories in all one-day matches would provide a common margin of victory suitable for analysis.     

Analytical approximations to predict performance measures of manufacturing systems with general distributions,job failures and parallel processing

Parallel processing is prevalent in many manufacturing and service systems (i.e. some components may have to wait for other components before the assembly can begin). It is also common to observe manufacturing systems that deal with multiple products, resources shared between different products, and circulation due to random part failures. An example of such a system configuration is observed at a facility equipped to assemble and test web servers. The primary objective of this research was to develop analytical approximations to predict performance measures of a system with the above characteristics and evaluate its accuracy. Manufacturing systems with general distributions, multiple products, job circulation due to failures, resource sharing, and a fork and join system (to model parallel processing of some assembly operations) were studied using the parametric decomposition approach. The different work centers (or stations) in the manufacturing system is modeled as a network of queues and the parametric decomposition approach is applied to decompose the network of queues into individual queues to estimate the performance measure of the system. Existing analytical formulations were modified and appropriate correction terms were added to the approximations to bridge the gap in the error between the analytical approximation and the simulation models. Random instances were generated and the flow times from the approximations and simulation models were compared. The experimental study conducted indicates that the analytical approximations along with the correction terms can serve as a good estimate for the flow times of the manufacturing systems with the above characteristics.     

Using a model of the performance measures in Soft Systems Methodology (SSM) to take action: a case study in health care

This paper uses a case study of a multidisciplinary colorectal cancer team in health care to explain how a model of performance measures can lead to debate and action in Soft System Methodology (SSM). This study gives a greater emphasis and role to the performance measures than currently given in typical SSM studies. Currently, the concept of performance measurement in SSM is in the form of a set of criteria used to judge the performance of the SSM model (the purposeful activity model). These performance criteria are definitions of efficacy, efficiency, effectiveness, ethicality and elegance. However, the use of performance measures within SSM is not clear and therefore criticized by some as nebulous. This paper uses a case study to explain how to involve the stakeholders in deriving a performance measurement model (PMM), which is a more detailed expansion of the performance criteria. The paper concludes with some reflections about how the PMM can fit in the SSM cycle, with two modes of practice put forward.     

The impact of unknown demand parameters on (R,S)-inventory control performance

For a given inventory control system and a known stationary demand pattern, it is relatively easy to calculate the safety factors needed to satisfy predetermined performance criteria. It is more or less customary to use these standard safety factors in practical situations as well. In practice, however, demand parameters are unknown, causing additional variation. Consequently, the performance of this standard approach generally stays below the desired level. Hence, the safety factors should be increased.This general phenomenon is studied here in some detail for an (R,S)-inventory control system with normal demand, using the two best-known service criteria. Simple exponential smoothing is used to estimate the unknown demand parameters. Using large simulation runs, new (constant) safety factors are found that do satisfy the given service levels.They are not suitable for practical use, however: long series of past observations usually are not available, while stationary demand is rare. Therefore, time-varying safety factors are presented that seem to perform well for normal demand with unknown parameters.     

The adoption of environmental and risk management practices: Relationships to environmental performance

The Strategic Goals Program sponsored by the United States Environmental Protection Agency which focuses on the Metal Finishing Industry is used to investigate some pertinent issues related to small manufacturing enterprises' environmental performance. Results from the initial years of this program are used to evaluate a number of hypotheses related to the relationship between environmental performance and adoption of environmental and risk management practices, especially among smaller organizations. The methodology uses unique structuring of data to determine temporal environmental performance using data envelopment analysis. Results show that early and increased investment in these practices and programs may not provide for better performance benefits. The findings have implications for environmental managers in smaller organizations and policy makers overseeing these types of organizations.     

The impact of data collection on fill rate performance in the (R,s, Q) inventory model

In this paper we consider the determination of the reorder point s in an (R, s, Q) inventory model subject to a fill rate service level constraint. We assume that the underlying demand process is a compound renewal process. We then derive an approximation method to compute the reorder level such that a target service level is achieved. Restrictions on the input parameters are given, within which this method is applicable. Moreover, we will investigate the effects on the fill rate performance in case the underlying demand process is indeed a compound renewal process, while the demand process is modelled as a discrete-time demand process. That is, the time axis is divided in time units (for example, days) and demands per time unit are independent and identically distributed random variables. It will be shown that smooth and erratic behaviour of the inter-arrival times have different impacts on the performance of the fill rate when demand is modelled as a discrete-time process and in case the underlying demand process is a compound renewal process.     

Environmental safety stock: The impacts of regulatory and voluntary control policies on production planning,inventory control,and environmental performance

This paper analyzes the impacts of different pollution control policies on a firm’s decisions of production planning and inventory control. Based on a stochastic model with both demand and environmental uncertainties, we derive the optimal policies of production planning and inventory control under both regulatory and voluntary pollution control approaches, and investigate their operational and environmental effects. We establish that the conventional wisdom which suggests that reduction of environmental waste at the end of a production process also decreases the stock and throughput levels of a production system is not necessarily true. Rather, a regulatory environmental standard that limits the total amount of waste may induce the firm to raise its planned stock level, which would lead to a higher expected amount of environmental wastes before the standard is enforced as well as environmental risks at other stages of the production process. The additional planned stock level, which is termed “environmental safety stock,” can be reversed by using the voluntary control approach that provides the firm with the flexibility to occasionally exceed the environmental standard. We also conduct numerical experiments to analyze the effects of different values of model parameters under different control approaches. The analytical results provide new insights to the impacts of a firm’s production and inventory decisions on the natural environment as well as to the choices of pollution control approaches by decision makers in both the private and public sectors.