About

Hummy Song is an Associate Professor of Operations, Information and Decisions at the Wharton School at the University of Pennsylvania, and also holds an appointment as Associate Professor of Health Care Management. She completed her undergraduate, master’s, and PhD studies at Harvard University. Her research focuses on improving the performance of service systems, with a particular emphasis on the health care sector. Her work examines factors related to patient flow and capacity management in health care delivery settings, including queue configurations, off-service placement, performance feedback, provider turnover, and team staffing. She utilizes large datasets derived from electronic health records, administrative databases, and surveys of the health care workforce, collaborating with hospitals and health care organizations in the U.S. and developing countries. Her research has been published in leading academic journals such as Management Science, Operations Research, and Health Services Research, and has appeared in Harvard Business Review. She has received media coverage from outlets including the Wall Street Journal, Reuters, and CBS News. Recognized for her contributions, she was named by Poets & Quants as one of the Top 50 Undergraduate Business Professors and received the 2022 POMS Early Career Research Accomplishments Award. She currently serves as an Associate Editor for Management Science, Operations Research, and Service Science.

Research topics

• Medicine
• Computer Science
• Internal medicine
• Economics
• Business
• Medical emergency
• Artificial Intelligence
• Computer network
• Environmental health
• Psychology
• Family medicine
• Pathology
• Operations research
• Economic growth
• Medical education
• Emergency medicine
• Obstetrics
• Operations management
• Industrial organization
• Mathematics
• Management
• Geography
• Microeconomics
• Nursing

Selected publications

• Inpatient to Outpatient Shifts in Surgical Care: Persistence of COVID-19 Era Changes and Socioeconomic Variations

  Medical Care Research and Review · 2025-12-06 · 1 citations

  articleOpen access

  The COVID-19 pandemic disrupted surgical care delivery, yet the extent to which shifts from inpatient to outpatient settings have persisted remains unclear. Using medical claims data from Independence Blue Cross (2018-2022), we examined changes in surgery settings across 102 procedures before the pandemic and during the 2 years following the suspension of elective surgeries. After 2 years, inpatient volumes decreased for 9 of the 20 most common pre-pandemic inpatient procedures, with corresponding increases in outpatient utilization. Hip and knee replacements experienced the most pronounced shifts, with inpatient shares falling by more than 40 percentage points. Patients from lower-income census tracts saw greater declines in overall procedure volumes (-6.0%) compared to those from higher-income areas (+5.2%). Total allowed amounts decreased for procedures with outpatient migration, while out-of-pocket costs remained stable. These findings suggest durable, post-pandemic shifts in surgical care delivery patterns, with potential implications for access, costs, and equity.

  PublisherDOI

• The Spillover Effects of Capacity Pooling in Hospitals

  Management Science · 2024-01-16 · 14 citations

  article

  Off-service placement is a common capacity-pooling strategy that hospitals utilize to address mismatches in supply and demand that arise from the day-to-day variation in patient demand. This strategy involves placing patients in a bed in a unit that is designated for another specialty service. Building on prior work that documents the negative first order effects of off-service placement on patients who are placed off service themselves, we quantify the spillover effects of this practice on patients who are actually placed on service. Using an estimation strategy that combines the Heckman correction procedure and a heteroskedasticity-based identification approach, we find that off-service placement has substantial negative spillover effects on the efficiency of care delivered to on-service patients. In particular, we find that a 10 percentage point increase in the level of off-service placement during a patient’s hospitalization is associated with a 10.9% increase in length of stay. Through a series of counterfactual analyses, we propose alternate routing and capacity-planning policies that could meaningfully improve the efficiency of care in the inpatient setting. This paper was accepted by Stefan Scholtes, healthcare management. Funding: This work was supported by Claude Marion Endowed Faculty Scholar Award; Fishman-Davidson Center for Service and Operations Management. Supplemental Material: The online appendix and data files are available at https://doi.org/10.1287/mnsc.2022.02202 .

  PublisherDOI

• To Each Their Own (Shifts): Incorporating Heterogeneous Worker Preferences into Shift Work Schedules

  SSRN Electronic Journal · 2024-01-01 · 3 citations

  articleOpen access
  PublisherDOI

• Queue Configurations and Operational Performance: An Interplay Between Customer Ownership and Queue Length Awareness

  Manufacturing & Service Operations Management · 2024-08-19 · 10 citations

  article1st authorCorresponding

  Problem definition: Contrary to traditional queueing theory, recent field studies in B2C services indicate that pooled queues may be less efficient than dedicated queues. Methodology/results: We use two online experiments in the healthcare delivery context to replicate this finding and assess the interplay of servers’ customer ownership and queue length awareness as potential underlying mechanisms. We operationalize customer ownership as the extent to which servers feel ownership toward their customers and queue length awareness as the extent to which servers are able to accurately quantify their number of customers. We find that, following a change in queue configuration, dedicated queues outperform pooled queues with respect to processing speed without sacrificing quality. The reduction in speed is partially mediated by the servers’ queue length awareness and partially suppressed by their ownership of customers in queue. The former is because servers turn out to be less likely to underestimate their load, which makes them work faster. The latter is because ownership of customers in queue may distract servers from the customer in service. When the queue configuration changes from a dedicated to a pooled one, the shorter processing times and higher levels of queue length awareness persist across the change, unlike the higher ownership of customers in the queue. Managerial implications: In discretionary service settings, switching to a dedicated queue is often beneficial in terms of operational performance, partly because the increased queue length awareness motivates servers to work faster; however, the increased degree of customer ownership of those in queue may distract them and result in a slowdown. Funding: This work was supported by the Wharton Behavioral Lab, the Claude Marion Endowed Faculty Scholar Award, the Wharton-INSEAD Alliance, and the Wharton Dean’s Research Fund. Supplemental Material: The online appendices are available at https://doi.org/10.1287/msom.2023.0202 .

  PublisherDOI

• “I Quit”: Schedule Volatility as a Driver of Voluntary Employee Turnover

  Manufacturing & Service Operations Management · 2023-03-15 · 28 citations

  articleSenior author

  Problem definition: Employers across many sectors of the economy have been fast to adopt variable work scheduling policies. The cost of this flexibility for employers is usually borne by employees, for whom unstable work schedules create several disruptions. In the context of home healthcare, we examine how employer-driven volatility in nurses’ schedules impacts their decision to voluntarily leave their job. Methodology/results: Using an instrumental variables approach, we causally identify the effect of schedule volatility on nurses’ voluntary turnover. We begin by constructing an operational measure of schedule volatility using time-stamped work log data from one of the largest home health agencies in the United States. Because this measure may be endogenous to the worker’s decision to quit, we instrument for schedule volatility using paid days off taken by other nurses in the same branch. We find that higher levels of schedule volatility substantially increase a worker’s likelihood of quitting. Specifically, a one-standard-deviation increase in schedule volatility increases the average worker’s propensity to quit on a given day by more than threefold. Translated into yearly terms, 30 days of high schedule volatility over the course of the year increases the average worker’s probability of quitting that year by 20%. Our policy simulations of counterfactual scheduling policies suggest that excess schedule volatility can explain a significant portion of voluntary turnover, and some interventions have the potential to substantially reduce workers’ daily propensity to quit. Managerial implications: This work contributes to the understanding of the extent to which employees value control over their own work schedules and are averse to volatile work schedules that are dictated by employers. Especially in the current environment where there is a growing emphasis on work-life balance and employee-driven flexibility, finding a way to support stable schedules could be important for employers to attract and retain workers. Funding: This work was supported by the National Research Service Award Postdoctoral Fellowship, the Wharton Dean's Research Fund, the Agency for Healthcare Research and Quality [T32 Grant 5T32HS26116], and the Claude Marion Endowed Faculty Scholar Award. Supplemental Material: The e-companion is available at https://doi.org/10.1287/msom.2023.1205 .

  PublisherDOI

• Geographic cohorting by clinical care team: a narrative review

  Annals of Palliative Medicine · 2023-04-13 · 5 citations

  reviewOpen access

  BACKGROUND AND OBJECTIVE: Geographic cohorting refers to localization of inpatients to designated hospital areas (typically a unit or a set of beds) based on specified criteria. One such criterion that has been commonly discussed and studied since the early days of the hospitalist movement in the US is a patient's assigned clinical care team. Because implementing cohorting of this type requires substantial operational investment, it is important to understand the benefits and the tradeoffs associated with bringing patients into closer spatial proximity with their full team of providers and allowing clinicians to work within a defined clinical space. METHODS: We conducted a narrative review of the evidence around geographic cohorting of patients by clinical care team. We performed a comprehensive search of the PubMed, Embase, Cinahl and Scopus databases, identifying relevant English language articles. We used an inductive approach to developing thematic domains for categorization of article content. KEY CONTENT AND FINDINGS: We reviewed eighteen articles published between 2008 and 2022, and identified four thematic outcomes domains: patient-centered outcomes, communication, efficiency, and satisfaction. The existing literature demonstrates associations with improved communication and staff satisfaction. The data regarding patient outcomes and overall work efficiency, on the other hand, are equivocal and, in general, limited by study methodology. CONCLUSIONS: Geographic cohorting of inpatients according to clinical care team offers some promise for improved workplace culture. More rigorously designed studies are needed, however, to understand its impact on patient outcomes, and there should be added attention paid to throughput metrics and tradeoffs that often limit its implementation.

  PublisherOA PDFDOI

• Multi-Channel Healthcare Operations: The Impact of Video Visits on the Usage of In-Person Care

  SSRN Electronic Journal · 2023-01-01 · 2 citations

  articleOpen access
  PublisherDOI

• The Relationship Between Scope of Practice Laws for Task Delegation and Nurse Turnover in Home Health

  Journal of the American Medical Directors Association · 2023-08-24 · 4 citations

  articleOpen access
  PublisherOA PDFDOI

• Leapfrogging for Last-mile Delivery in Health Care

  SSRN Electronic Journal · 2022 · 10 citations

  Senior authorCorresponding
  • Business
  • Medical emergency
  • Medicine
  PublisherDOI

• Learning in Temporary Teams: The Varying Effects of Partner Exposure by Team Member Role

  Organization Science · 2022 · 43 citations

  • Computer Science
  • Psychology
  • Medical education

  In many workplaces, temporary teams convene to coordinate complex work, despite team members having not worked together before. Most related research has found consistent performance benefits when members of temporary teams work together multiple times (team familiarity). Recent work in this area broke new conceptual ground by instead exploring the learning and performance benefits that team members gain by being exposed to many new partners (partner exposure). In contrast to that new work that examined partner exposure between team members who are peers, in this paper, we extend this research by developing and testing theory about the performance effects of partner exposure for team members whose roles are differentiated by authority and skill. We use visit-level data from a hospital emergency department and leverage the ad hoc assignment of attendings, nurses, and residents to teams and the round-robin assignment of patients to these teams as our identification strategy. We find a negative performance effect of both nurses’ and resident trainees’ partner exposure to more attendings and of attendings’ and nurses’ exposure to more residents. In contrast, both attendings and residents experience a positive impact on performance from working with more nurses. The respective effects of residents working with more attendings and with more nurses is attenuated on patient cases with more structured workflows. Our results suggest that interactions with team members in decision-executing roles, as opposed to decision-initiating roles, is an important but often unrecognized part of disciplinary training and team learning. Funding: This work was supported by the New Faculty Startup Fund from Seoul National University; Harvard Business School; Stanford Center for Work, Technology, and Organization; and Stanford Center for Designing Organizational Change. Supplemental Material: The online supplement is available at https://doi.org/10.1287/orsc.2022.1585 .

  PublisherDOI

Frequent coauthors

• Guy David

  University of Pennsylvania

  12 shared

• Anita L. Tucker

  Boston University

  9 shared

• Alon Bergman

  University of Pennsylvania

  7 shared

• Alyna T. Chien

  Harvard University

  7 shared

• Guillaume Roels

  INSEAD

  6 shared

• Jia-Jie Zhu

  6 shared

• Antoinette S. Peters

  Harvard Pilgrim Health Care

  6 shared

• Julia Martin

  6 shared

Labs

• Operations, Information and Decisions DepartmentPI

Awards & honors

• 1st Place, 2025 POMS College of Sustainable Operations Best…
• 2nd Place, 2023 INFORMS Public Sector Operations Research Be…
• Finalist, INFORMS Health Applications Society Best Student P…
• Poets & Quants Top 50 Undergraduate Professors (2022)
• Winner, POMS Early Career Research Accomplishments Award (20…