Sean Willems

Sean Willems, Graves, S. C. B. T. Tomlin (2026), Supply Chain Challenges In The Post- Covid Era, .

Abstract: In this paper, we reflect on the supply chain issues and operational challenges that we experienced through the various stages of the Covid‐19 pandemic. We identify some phenomena that were attributable in some way to the pandemic, and apply core principles of operations management, and a simple numerical model, to explain and understand their occurrence. We highlight some key lessons and discuss implications for supply chain design and planning, to prepare for the next global disruption.

Sean Willems, Brennan, M. Dyer, S. Salvia, J. Segal, L. Serino, E. Steil, J. (2026), The City of Boston Sites Policy Interventions to Address Disparate Car-Crash Risk, .

Abstract: Unsegmented emergency medical services (EMS) data obscure whether certain patients need care more than others, historically limiting cities from pursuing some preventative health interventions. The operations community has long pioneered prescriptive analytics for EMS response using data on incident location and time though novel descriptive analytics that segment demand by patient demographics and exposure type can inform preventative policy efforts, such as making capital investments and conducting outreach to lessen the risk of people being struck by motorists. Segmentation is the analytics response to demand heterogeneity in operations. By linking ambulance records to patient age and neighborhood socioeconomic characteristics, Boston EMS and partner agencies developed a data-driven approach to segment demand and guide siting preventative interventions. The approach parses demand by the demographics of patients struck by motorists (age and neighborhood socioeconomic status) along with the exposure type (walking or cycling during school commute hours) and the location where they were struck. The process overcomes long-standing data handling, computational, and conceptual barriers. Traffic crashes disproportionately affect children walking and cycling to school who reside in Boston’s poorest areas. The city used these findings to locate six initial capital projects and identify seven schools in the most affected areas in which to conduct outreach. The city also expanded data sharing between agencies to enable regular preventative work. Compared with the current resource allocation process, this socioeconomically sensitive segmentation that captures the profile of patients struck by motorists elevates disadvantaged neighborhoods in the urban planning process.

Sean Willems, Klosterhalfen, S.T. D. Dittmar (2023), Strategic Safety Stock Placement in Supply Chains With Expediting, .

Abstract: Numerous documented implementations demonstrate the guaranteed-service (GS) model of safety stock optimization has applicability to practice. The standard GS (S-GS) model employs safety stock as the only countermeasure to satisfy a specified demand bound, assuming any demand in excess of the bound will be addressed by countermeasures which are not modeled. We extend the S-GS model to explicitly include expediting as a second countermeasure. Thus, our two-countermeasure GS (2C-GS) formulation addresses more demand variability explicitly than the S-GS model. We characterize a stage’s optimal base-stock level as the maximum of two base-stock calculations, and show how the resulting optimization problem can be efficiently solved using existing GS solution techniques. For normally distributed demand, we analytically characterize when the S- and 2C-GS approaches deploy different configurations of safety stock. For a series of numerical experiments, we find that the 2C-GS model places safety stocks at more stages than the S-GS model. When compared to the 2C-GS solution, the suggested safety stock positioning of the S-GS approach results in an average cost increase of 7%, and a maximum of 42%, in real-world supply chain settings. Furthermore, the benefits from expediting increase when downstream stages have greater expediting capability.

Sean Willems, Lo, A. W. B. Stevens (2022), World of Edcraft: Challenges And Opportunities Of Online Teaching, .

Abstract: Online teaching at higher educational institutions has become a much higher priority in the face of the COVID-19 pandemic, but most faculty and staff at these institutions are ill-prepared to adapt their teaching methods and content to this new medium. This article guides the reader through three teaching studios developed for online synchronous teaching to very different student populations: a large (90-student) graduate-level healthcare finance course at MIT, an even larger (200-student) undergraduate-level statistics course at the University of Tennessee, Knoxville, and a medium-sized (50-student) graduate-level operations management course at MIT. As we began building these studios, we found few applications in higher-education settings to rely on. Instead, we borrowed ideas and tools from the gaming community. Since different faculty will have different teaching styles and objectives, we have adopted a tour guide approach that describes the intent of each studio design, a complete listing of the software and hardware used in the studio, and a representative example of what the studio can achieve in practice. We conclude by documenting how other faculty have produced minimally sufficient studios for online teaching.

Sean Willems, Letizia, P. J. Jia (2022), Supply Chain Coordination with Information Design, .

Abstract: We consider the coordination of a supplier–retailer supply chain where, in addition to classical contract considerations, a supplier decides the adoption of an information structure (IS) for the supply chain, with a higher-quality IS allowing the supply chain parties to obtain a more accurate demand forecast. Because a wholesale price contract cannot coordinate the supply chain due to misaligned incentives of supply chain parties, we explore what common coordinating contracts in the classical coordination literature can continue coordinating the supply chain with the IS adoption. Interestingly, our analysis appears to reveal the power of simplicity: some simple classical coordinating contracts (e.g., the buy-back and revenue-sharing contracts), though not designed with the IS consideration, still coordinate the supply chain, whereas other more complicated classical contracts (e.g., the quantity flexibility and sales rebate contracts) fail to do so. We derive a general condition for supply chain coordination and show that any contract with a newsvendor-like transfer payment can coordinate the supply chain.