Assistant Professor of Biostatistics
Siyu Heng, PhD is an Assistant Professor in the Department of Biostatistics, with an interest in both methodology research and applied research. His areas of expertise are in causal inference, health data science, observational studies, randomized trials, sensitivity analysis, instrumental variables, measurement error, and in survey data and their applications in public health.
Dr. Heng’s research has been published in the Journal of the Royal Statistical Society and in Physical Review, among others. He has been recognized with several awards, including the IPUMS Global Health Research Award for the Best Student Paper; the Lawrence D. Brown Best Paper Award; the ASA Mental Health Statistics Section Student Paper Award; the ENAR Distinguished Student Paper Award; the NESS Student Research Award, and the Wellcome Trust Data Reuse Prize.
Dr. Heng received his PhD in applied mathematics and computational science from the University of Pennsylvania, and his BA in statistics from Nanjing University.
PhD Candidate, Applied Mathematics and Computational Science (Statistics Track) University of PennsylvaniaBS, Mathematics, Nanjing University
IPUMS Global Health Research Award for the Best Student Paper, Integrated Public Use Microdata Series (2021)IMS Hannan Graduate Student Travel Award, Institute of Mathematical Statistics (2021)ASA Mental Health Statistics Section Student Paper Award, American Statistical Association Section on Mental Health Statistics (2021)ENAR Distinguished Student Paper Award, International Biometric Society Eastern North American Region (2021)Wellcome Trust Data Reuse Prize: Malaria, Wellcome Trust (2019)Benjamin Franklin Fellowship, University of Pennsylvania School of Arts and Sciences (201620172018)
Causal InferenceEpidemiologyGlobal HealthHealth EquityInstrumental VariablesObservational StudiesPublic Health PolicyRandomized ExperimentationSocial Sciences
SOCIAL DISTANCING AND COVID-19: RANDOMIZATION INFERENCE FOR A STRUCTURED DOSE-RESPONSE RELATIONSHIP
Testing Biased Randomization Assumptions and Quantifying Imperfect Matching and Residual Confounding in Matched Observational Studies
The Central Role of the Propensity Score in Sensitivity Analysis for Matched Observational Studies
Bridging preference-based instrumental variable studies and cluster-randomized encouragement experiments: Study design, noncompliance, and average cluster effect ratio
Hemoglobin Levels among Male Agricultural Workers: Analyses from the Demographic and Health Surveys to Investigate a Marker for Chronic Kidney Disease of Uncertain Etiology
Association between Transesophageal Echocardiography and Clinical Outcomes after Coronary Artery Bypass Graft SurgeryMacKay, E. J., Zhang, B., Heng, S., Ye, T., Neuman, M. D., Augoustides, J. G., Feinman, J. W., Desai, N. D., & Groeneveld, P. W. (n.d.).
Journal titleJournal of the American Society of Echocardiography
Page(s)571-581AbstractBackground: Coronary artery bypass graft (CABG) surgery is the most widely performed cardiac surgery in the United States. Transesophageal echocardiography (TEE) is frequently used in a variety of cardiac surgical procedures, but its clinical benefit in isolated CABG surgery is unclear, and guidelines remain indeterminate. The aim of this study was to compare clinical outcomes among patients undergoing isolated CABG surgery with versus without TEE in order to test the hypothesis that TEE would be associated with improved clinical outcomes after CABG surgery. Methods: A matched retrospective cohort study was conducted among Medicare beneficiaries undergoing isolated CABG surgery with versus without intraoperative monitoring using TEE in the United States. The primary analysis was a near/far instrumental variable match that paired hospitals with similar characteristics and patient populations but with opposing probabilities for using TEE in CABG surgery. Outcomes included 30-day mortality, a composite outcome of stroke or 30-day mortality, length of hospitalization, and incidence of esophageal perforation. Results: Of 114,871 patients undergoing isolated CABG surgery, 65,471 (57%) underwent TEE and 49,400 (43%) did not. Hospital-level instrumental variable matched analysis demonstrated that among the subset of 968 matched hospitals, TEE receipt was associated with lower 30-day mortality (3.7% vs 4.9%, P <.001), a lower incidence of the composite outcome of stroke or 30-day mortality (4.5% vs 5.6%, P <.001), no difference in length of hospitalization (10.32 vs 10.52 days, P =.26), and no difference in the incidence of esophageal perforation (0.01% vs 0.01%, P =.63). These results were replicated in surgeon-level and patient-level matched-pair instrumental variable analyses, and all analyses were robust to sensitivity analyses that tested for biases introduced by unmeasured confounding. Conclusions: The findings from this study suggest that TEE may offer a clinical benefit to cardiac surgical patients undergoing isolated CABG surgery.
Increasing power for observational studies of aberrant response: An adaptive approach
Relationship between changing malaria burden and low birth weight in sub-saharan africa: A difference-in-differences study via a pair-of-pairs approachHeng, S., O’meara, W. P., Simmons, R. A., & Small, D. S. (n.d.).
Volume10AbstractBackground: According to the World Health Organization (WHO), in 2018, an estimated 228 million malaria cases occurred worldwide with most cases occurring in sub-Saharan Africa. Scale-up of vector control tools coupled with increased access to diagnosis and effective treatment has resulted in a large decline in malaria prevalence in some areas, but other areas have seen little change. Although interventional studies demonstrate that preventing malaria during pregnancy can reduce the rate of low birth weight (i.e. child’s birth weight <2500 g), it remains unknown whether natural changes in parasite transmission and malaria burden can improve birth outcomes. Methods: We conducted an observational study of the effect of changing malaria burden on low birth weight using data from 18,112 births in 19 countries in sub-Saharan African countries during the years 2000–2015. Specifically, we conducted a difference-in-differences study via a pair-of-pairs matching approach using the fact that some sub-Saharan areas experienced sharp drops in malaria prevalence and some experienced little change. Results: A malaria prevalence decline from a high rate (Plasmodium falciparum parasite rate in children aged 2-up-to-10 (i.e. PfPR2-10) > 0.4) to a low rate (PfPR2-10 < 0.2) is estimated to reduce the rate of low birth weight by 1.48 percentage points (95% confidence interval: 3.70 percentage points reduction, 0.74 percentage points increase), which is a 17% reduction in the low birth weight rate compared to the average (8.6%) in our study population with observed birth weight records (1.48/8.6 » 17%). When focusing on first pregnancies, a decline in malaria prevalence from high to low is estimated to have a greater impact on the low birth weight rate than for all births: 3.73 percentage points (95% confidence interval: 9.11 percentage points reduction, 1.64 percentage points increase). Conclusions: Although the confidence intervals cannot rule out the possibility of no effect at the 95% confidence level, the concurrence between our primary analysis, secondary analyses, and sensitivity analyses, and the magnitude of the effect size, contribute to the weight of the evidence suggesting that declining malaria burden can potentially substantially reduce the low birth weight rate at the community level in sub-Saharan Africa, particularly among firstborns. The novel statistical methodology developed in this article–a pair-of-pairs approach to a difference-in-differences study–could be useful for many settings in which different units are observed at different times.
SHARPENING THE ROSENBAUM SENSITIVITY BOUNDS TO ADDRESS CONCERNS ABOUT INTERACTIONS BETWEEN OBSERVED AND UNOBSERVED COVARIATES
Finding the strength in a weak instrument in a study of cognitive outcomes produced by Catholic high schoolsHeng, S., Small, D. S., & Rosenbaum, P. R. (n.d.).
Journal titleJournal of the Royal Statistical Society. Series A: Statistics in Society
Page(s)935-958AbstractWe show that the strength of an instrument is incompletely characterized by the proportion of compliers, and we propose and evaluate new methods that extract more information from certain settings with comparatively few compliers. Specifically, we demonstrate that, for a fixed small proportion of compliers, the presence of an equal number of always-takers and never-takers weakens an instrument, whereas the absence of always-takers or, equivalently, the absence of never-takers strengthens an instrument. In this statement, the strength of an instrument refers to its ability to recognize and reject a false hypothesis about a structural parameter. Equivalently, the strength of an instrument refers to its ability to exclude from a confidence interval a false value of a structural parameter. This ability is measured by the Bahadur efficiency of a test that assumes that the instrument is flawless, or the Bahadur efficiency of a sensitivity analysis that assumes that the instrument may be somewhat biased. When there are few compliers, the outcomes for most people are unaffected by fluctuations in the instrument, so most of the information about the treatment effect is contained in the tail of the distribution of the outcomes. Exploiting this fact, we propose new methods that emphasize the affected portion of the distribution of outcomes, thereby extracting more information from studies with few compliers. Studies of the effects of Catholic high schools on academic test performance have used ‘being Catholic’ as an instrument for ‘attending a Catholic high school’, and the application concerns such a comparison using the US National Educational Longitudinal Study. Most Catholics did not attend Catholic school, so there are few compliers, but it was rare for non-Catholics to attend Catholic school, so there are very few always-takers.
Can phoretic particles swim in two dimensions?Sondak, D., Hawley, C., Heng, S., Vinsonhaler, R., Lauga, E., & Thiffeault, J. L. (n.d.).
Journal titlePhysical Review E
Issue6AbstractArtificial phoretic particles swim using self-generated gradients in chemical species (self-diffusiophoresis) or charges and currents (self-electrophoresis). These particles can be used to study the physics of collective motion in active matter and might have promising applications in bioengineering. In the case of self-diffusiophoresis, the classical physical model relies on a steady solution of the diffusion equation, from which chemical gradients, phoretic flows, and ultimately the swimming velocity may be derived. Motivated by disk-shaped particles in thin films and under confinement, we examine the extension to two dimensions. Because the two-dimensional diffusion equation lacks a steady state with the correct boundary conditions, Laplace transforms must be used to study the long-time behavior of the problem and determine the swimming velocity. For fixed chemical fluxes on the particle surface, we find that the swimming velocity ultimately always decays logarithmically in time. In the case of finite Péclet numbers, we solve the full advection-diffusion equation numerically and show that this decay can be avoided by the particle moving to regions of unconsumed reactant. Finite advection thus regularizes the two-dimensional phoretic problem.