Publications
Ang, R. (2025). Expanded Prescription Coverage and Opioid Use Disorders: Evidence from Medicare Part D. Economics & Human Biology, 59, 101536. doi: 10.1016/j.ehb.2025.101536
Kim, K., Lee, J., Albis, M., & Ang, R. (2021). Benefits and Spillover Effects of Infrastructure: A Spatial Econometric Approach. East Asian Economic Review, 25(1), pp. 3-31. doi: 10.11644/KIEP.EAER.2021.25.1.389
Kim, K., Lee, J., Albis, M., & Ang, R. (2020). Benefits and Spillover Effects of Infrastructure: A Spatial Econometric Approach. In B. Susantono, & C.Y. Park (Eds.), Future of Regional Cooperation in Asia and the Pacific (pp. 62-94). Asian Development Bank. doi: 10.22617/TCS200336-2
Paderon, M.M., & Ang, R. (2019). Possible Effects of China’s Belt and Road Initiative on Philippine Trade and Investments. Philippine Journal of Development, 44(2), pp. 36-49.
Working Papers
When the Clock Ticks: Causal Effects of Surgical Delay on Inpatient Outcomes (job market paper; previously, "The Weekend Effect on Inpatient Outcomes: Evidence from Delayed Procedures in Emergency Admission")
Abtract: I estimate the causal effect of surgical delays on inpatient outcomes using weekend admission as an instrument for time to procedure. I use the Nationwide Inpatient Sample from 1998 to 2011 and focus on emergency admissions for acute appendicitis, acute cholecystitis, and obstructed hernia. A two-stage least squares design exploits weekend admission as a source of plausibly exogenous variation in treatment timing, addressing confounding from unobserved illness severity and hospital selection. In the first stage, weekend admission delays surgery by 0.18 days for acute cholecystitis patients (12.35 percent of the mean) and by 0.12 days for obstructed hernia patients (12.46 percent). In the second stage, each additional day of delay increases length of stay by 0.76 days for cholecystitis patients (20.94 percent of the mean) and 1.55 days for hernia patients (31.19 percent), and for hernia patients also raises the risk of postoperative wound complications by 0.027 percentage points (146 percent relative to the mean). No second-stage effect is detected for appendicitis, consistent with the weak first stage. Heterogeneity analyses show larger effects in rural, government, and low-income-serving hospitals, as well as differences across patient subgroups by payer status, race, and income. A back-of-the-envelope calculation suggests that weekend-related delays for cholecystitis and hernia admissions generate roughly 10,558 excess inpatient days annually, equivalent to about $27.5 million in additional hospitalization costs. These findings provide new causal evidence on the consequences of delayed surgical treatment and underscore the efficiency and equity gains from improving timely access to acute surgical care.
Medicare Part D and Hospital Admissions Due to Antimicrobial Resistance (R&R, Health Economics)
Abstract: Antimicrobial resistance has been growing rapidly in the United States in recent years despite government efforts to control its outbreak. Both under and overutilization of prescribed medications can lead to an increase in antimicrobial resistance. The introduction of Medicare Part D in 2006 led to an increase in prescription drug coverage, including antimicrobials, for the elderly. If cost barriers had led to underutilization of prescriptions among those without previous prescription coverage, then Medicare Part D may reduce antimicrobial resistance. On the other hand, if Medicare Part D encourages over-utilization of prescriptions, then an unintended consequence may be an increase in antimicrobial resistance. Using data from the Nationwide Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality for years 2004 to 2011 and a difference-in-differences identification strategy, I estimate the net effect of Medicare Part D on the incidence of inpatient discharges due to antimicrobial resistance among the Medicare-eligible population. Results show that the incidence of antimicrobial resistance among the elderly as measured by inpatient discharges decreased after Medicare Part D implementation.
Automation and Diverging Health Risks (with Giseong Kim, Soojin Kim, and Mike Pesko) (under review)
Abstract: This paper examines the impact of automation on workers’ health risks, using occupational injury and hospitalization data. We first document that automation leads to a divergence in the severity of occupational health risks. Utilizing data on nonfatal and fatal workplace injuries, we show that while automation reduces nonfatal occupational injury incidence, it increases fatal occupational injury incidence. Secondly, the disparity of health risks across age groups has widened due to automation. Hospital discharge data suggests that overall hospitalizations due to injuries and despair-related conditions (e.g., substance abuse) have declined in commuting zones with higher automation exposure. Yet, the benefits are concentrated among young workers, while middle-aged workers exposed to automation experience increased hospitalizations, particularly due to despair-related conditions. Combining the empirical estimates of nonfatal and fatal injury incidence, a back-of-the-envelope calculation suggests that workplace automation overall provides significant, health-driven economic benefits. However, the rise in fatal injuries offsets between 14% and 27% of economic benefits from the reduction of nonfatal injuries. In summary, automation improves workplace safety on average, but it shifts the distribution of accidents away from minor injuries towards high-impact failures and disproportionately reduces hospitalizations for younger workers while potentially increasing risks for older workers.
The Affordable Care Act and Hospital-Acquired Infections
Abstract: In October 2014, the United States government implemented Section 3008 of the Affordable Care Act (ACA), which imposes a 1 percent reduction in the Medicare reimbursements of hospitals that perform poorly based on a hospital-acquired infection (HAI) measure. A limited body of literature evaluates the impact of this policy in a primarily descriptive manner. Using patient discharge data from the National Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality and a difference-in-differences identification strategy, I contribute to the literature by estimating the causal effects this ACA provision had on the incidence of HAIs. Results suggest that the policy reduced the likelihood of acquiring an infection, with effects varying by HAI type. In addition, I find a general reduction in the likelihood of a HAI for whites, while the effects by gender or age vary on HAI type.
Works In Progress
Effects of the Affordable Care Act’s Medicaid Expansion on Physician Residency Programs (with Sukriti Beniwal)
The Medicaid Expansion and Graduate Medical Education: Hospital-Level Evidence from 2010–2019 (with Hussain Hadah)
Remittances and Disaster Recovery: Evidence from Philippine Fiestas (with Radine Rafols)