Seminar Series
Title
A Copula Joint Model to Address Endogeneity in the Relationship between ED Length of Stay and Readmission
Speaker
Dr. Guanjie Lyu
Time and Date
12 – 1 pm, Thursday, Nov 6, 2025
Location
MS teams: Join the meeting now
Bio
Dr. Guanjie Lyu is a Postdoctoral Fellow in the Department of Community Health and Epidemiology at Dalhousie University, working under the supervision of Dr. Cindy Feng. He earned his PhD in Statistics from the University of Windsor in 2024. Dr. Lyu’s research focuses on Bernstein polynomials and copula modeling, with broad applications in statistics and data analysis. His work spans both methodological development and applied problems, with a particular interest in dependence modeling and joint modeling of complex health data.
Professional Profile: https://guanjielyu.github.io/
Synopsis
The complex relationship between a patient's emergency department (ED) length of stay (LOS) and their subsequent ED readmission risk is a significant challenge in health services research. This presentation will show how to address the endogeneity of LOS, where unobserved factors can bias traditional models. We propose a novel framework using a copula joint model to simultaneously investigate this relationship and account for endogeneity. Our approach uses a continuous smooth function to capture the non-linear effect of LOS, revealing a sharply increasing risk for very short stays that then plateaus for intermediate stays. We validate our model using real-world ED data from Nova Scotia, Canada. A comprehensive simulation study compares our copula joint model against separate and two-stage regression approaches. The results demonstrate the superior performance and more accurate parameter estimates of the copula model, highlighting its power as a flexible statistical tool for analyzing outcomes with complex dependencies and endogeneity.
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Title
Complexity and Health Research
Speaker
Dr. Adrain Levy
Time and Date
12pm – 1pm
Thursday, December 11, 2025
Location
MS Teams : Join the meeting now
Bio
Adrian R. Levy PhD is a professor in the Department of Epidemiology and Community Health at Dalhousie University. His research focuses on improving the health of individuals and of populations. His research focuses on improving delivery of rapid access to high-quality, cost-effective and equitable health care. He is an Academic Editor at PLOS Complex Systems. He is author of over 60 peer reviewed publications and is the editor of two volumes on the Springer Handbook of Health Services Research: Comparative Effectiveness Research and Health Services Evaluation. He has been an Academic Editor for Health Research at PLOS Complex Systems since 2023.
Dr Adrian R. Levy, Ph. D., est professeur titulaire dans le département d’épidémiologie et de santé communautaire de l’Université de Dalhousie. Ses activités universitaires touchent à la recherche en services de santé. Il est l’auteur de plus de 140 publications avec comité de lecture et éditeur des manuels Springer consacrés à la recherche sur les services de la santé: Comparative Effectiveness Research et Health Services Evaluation. Il est rédacteur académique pour la recherche en santé chez PLOS Complex Systems depuis 2023.
Synopsis
Ensuring rapid access to high quality, affordable and equitable health care remains a central goal in Canada and globally. Yet, citizens of Canada and of other countries often suffer thorough suboptimal care, health authorities struggle to deliver more care with fewer resources, and governments vacillate between policies that alternatively centralize and decentralize health services. For example, the 2023 IPSOS Global Health Services Monitor survey in 31 countries documented increasing concerns along about quality, access, affordability and equity. The Economist points to the deterioration since the COVID-19 pandemic as a global “collapse in the quality of health care”. This phenomenon cuts across countries with different system structures workforce and structural capacity, different sources of remuneration and organization, different relative and absolute expenditures on health care and social spending, and different distributions of age, sex, and other demographic determinants of health.
To address these long-standing challenges, some 25 years ago, health service researchers began asserting that the new field of complexity sciences could provide solutions that meaningfully improve health outcomes. Despite these claims, in the many books and articles that have been written on the topic over the interval, no one has been able to quantitatively demonstrate how complexity works in a health care system.
In this presentation, I provide a brief introduction to complexity research alongside worked examples in different areas of health research. I conclude by speculating about fruitful directions for strengthening the field of health services research in light of complexity sciences.