DOCSLIB.ORG

Randomized Trial Shows Healthcare Payment Reform Has Equal-Sized Spillover Effects on Patients Not INAUGURAL ARTICLE Targeted by Reform

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Randomized Trial Shows Healthcare Payment Reform Has Equal-Sized Spillover Effects on Patients Not INAUGURAL ARTICLE Targeted by Reform Randomized trial shows healthcare payment reform has equal-sized spillover effects on patients not INAUGURAL ARTICLE targeted by reform Liran Einava,b, Amy Finkelsteinb,c,1, Yunan Jid, and Neale Mahoneya,b aDepartment of Economics, Stanford University, Stanford, CA 94305; bNational Bureau of Economic Research, Cambridge, MA 02138; cDepartment of Economics, Massachusetts Institute of Technology, Cambridge, MA 02139; and dGraduate School of Arts and Sciences, Harvard University, Cambridge, MA 02138 This contribution is part of the special series of Inaugural Articles by members of the National Academy of Sciences elected in 2018. Contributed by Amy Finkelstein, June 9, 2020 (sent for review March 16, 2020; reviewed by Jeffrey Clemens and Craig Garthwaite) Changes in the way health insurers pay healthcare providers may group, Medicare continues to reimburse providers under the sta- not only directly affect the insurer’s patients but may also affect tus quo fee-for-service system in which each provider receives a patients covered by other insurers. We provide evidence of such separate payment based on the amount of care delivered. spillovers in the context of a nationwide Medicare bundled pay- In the first 2 years of the program, about 400,000 patients and ment reform that was implemented in some areas of the country 1,500 hospitals were assigned to the treatment or control group. but not in others, via random assignment. We estimate that the Prior work has examined the direct impact of this bundled pay- payment reform—which targeted traditional Medicare patients— ment reform on targeted TM patients and estimated a ∼3% had effects of similar magnitude on the healthcare experience of decline in TM spending, driven predominantly by reduced dis- nontargeted, privately insured Medicare Advantage patients. We charges from the hospital to postacute care facilities, particularly discuss the implications of these findings for estimates of the im- skilled nursing facilities (1–5). pact of healthcare payment reforms and more generally for the We take advantage of the random assignment to study the design of healthcare policy. spillover impacts of this payment reform on patients who are covered by private insurers through the Medicare Advantage ECONOMIC SCIENCES bundled payments | healthcare | randomized controlled trial | spillover (MA) program, which provides private insurance coverage in lieu of TM to about one-third of Medicare-eligible enrollees. Our n the US healthcare system, most doctors and hospitals treat work builds on Wilcock et al. (6) and Meyers et al. (7), who were Ipatients that are covered by multiple health insurers. This the first to document spillovers of this program onto MA. We raises the possibility that a change in the way one health insurer enrich this analysis by examining heterogeneity across hospitals pays healthcare providers may not only affect the healthcare and by considering implications for healthcare payment reform. received by its own patients but could also affect the healthcare We study the direct effect on TM patients and spillover effects on received by patients covered by other insurers. Such spillovers MA patients using data from CMS. These data provide compre- could potentially have the same or opposite sign as the direct hensive claims-level information for TM patients and encounter- effect of the payment reform. To the extent they exist, spillovers level information for MA patients. Although not as detailed, the have implications for estimates of the impact of healthcare payment reforms and for the design of healthcare payment Significance policy. Yet, credibly estimating spillovers is challenging. In the ca- In the US healthcare system, most medical providers treat pa- nonical research design, which compares outcomes for directly tients covered by multiple insurers. As a result, changes in the targeted patients to outcomes for nontargeted patients, spill- way one health insurer pays for medical services could, by overs cannot be identified. When a research design does permit changing provider behavior, spill over onto patients covered by the identification of spillovers, a skeptical reader may interpret other insurers. In this article, we present evidence of such effects on nontargeted patients as evidence of a flawed research spillovers in the context of a large Medicare payment reform design, rather than evidence of spillovers. For good reason, that was implemented in some areas of the country but not in therefore, the bar for credibly identifying spillovers is high. others, via random assignment. We show that the payment In this article, we estimate spillovers from a Medicare payment reform had effects of similar magnitude on both the directly reform for hip and knee replacement that directly affected patients covered patients and on patients covered by other insurers. in the traditional Medicare (TM) program. This program provides We discuss implications of these findings for our interpre- an ideal setting to study spillovers because it was implemented via tation of existing estimates as well as for the design of random assignment in some areas of the country and not others, healthcare policy. and because it targets enough patients to potentially affect non- targeted patients as well. Author contributions: L.E., A.F., Y.J., and N.M. designed research, performed research, In particular, the program, known as Comprehensive Care for analyzed data, and wrote the paper. Joint Replacement (CJR), was designed and implemented in 2016 Reviewers: J.C., University of California San Diego; and C.G., Northwestern University. by the Centers for Medicare and Medicaid Services (CMS) as a The authors declare no competing interest. nationwide randomized trial. Randomization took place at the This open access article is distributed under Creative Commons Attribution-NonCommercial- metropolitan statistical area (MSA) level, with 67 MSAs randomly NoDerivatives License 4.0 (CC BY-NC-ND). assigned to treatment and 104 MSAs randomly assigned to con- See Profile on page 18909. trol. In the treatment group, Medicare makes a single bundled 1To whom correspondence may be addressed. Email: [email protected]. payment to hospitals for all services related to the episode of care, This article contains supporting information online at https://www.pnas.org/lookup/suppl/ including the initial hospital stay and subsequent care by other doi:10.1073/pnas.2004759117/-/DCSupplemental. medical providers during the recovery period. In the control First published July 27, 2020. www.pnas.org/cgi/doi/10.1073/pnas.2004759117 PNAS | August 11, 2020 | vol. 117 | no. 32 | 18939–18947 Downloaded by guest on September 25, 2021 data on MA patients still allow us to quantify spillovers along sev- Setting, Data, and Framework eral important margins. Setting. We study a payment reform in the TM program. Medi- Our results reveal spillover effects of the same sign and care, the US public health insurance program for the elderly and magnitude as the direct effects. For nontargeted MA patients, disabled, had about 60 million enrollees and $731 billion in an- we estimate that the payment reform reduces discharges to nual spending in 2018 (20, 21). About two-thirds of these postacute care facilities, such as skilled nursing facilities, by a enrollees are covered by the TM program, which offers a publicly statistically significant 3.3 percentage points, or about 12%. This administered insurance product. The remaining one-third of average spillover effect is remarkably similar to the average di- Medicare-eligible enrollees opt out of TM and enroll in the MA rect effect on TM patients. We also estimate a strong, positive program, where they are covered by private insurance plans. correlation between the direct effects and the spillover effects at Private insurers in MA are paid a fixed (risk-adjusted) monthly the hospital level: Hospitals with larger direct effects on the amount by Medicare for each beneficiary they enroll (21). discharge destination for TM patients also have larger spillover Under TM, providers have been paid primarily on a fee-for- effects on the discharge destination for MA patients. The effects— service basis, in which providers are reimbursed based on claims both direct and indirect—tend to be larger for hospitals with a submitted for medical services. For instance, for a patient un- large number of directly affected patients and for higher-quality dergoing hip replacement, Medicare would make separate pay- hospitals. ments to the hospital for the initial hospital stay, to the surgeon Our findings have implications for the optimal design of for performing the procedure and for each postoperative visit, to healthcare payment policies. When health insurers separately the skilled nursing facility for postacute care, and to the equip- ment owner for the rental of a wheelchair during the recovery design payment policies, they may not take into account the period. Moreover, within most of these categories, the payment spillovers to other patients. As a result, the separately designed would depend on the specific services provided.* payment policies may jointly result in suboptimal incentives for A key, well-appreciated concern with such fee-for-service healthcare providers, even when the policies are individually payments is that they may encourage providers to deliver care optimal. In other words, this is a classic case of what economists that has low or little value to the patient. Patients have to pay call externalities. only a small
Load more

Recommended publications
  • Detecting Spillover Effects: Design and Analysis of Multilevel Experiments
    This is a preprint of an article published in [Sinclair, Betsy, Margaret McConnell, and Donald P. Green. 2012. Detecting Spillover Effects: Design and Analysis of Multi-level Experiments. American Journal of Political Science 56: 1055-1069]. Pagination of this preprint may differ slightly from the published version. Detecting Spillover Effects: Design and Analysis of Multilevel Experiments Betsy Sinclair University of Chicago Margaret McConnell Harvard University Donald P. Green Columbia University Interpersonal communication presents a methodological challenge and a research opportunity for researchers involved infield experiments. The challenge is that communication among subjects blurs the line between treatment and control conditions. When treatment effects are transmitted from subject to subject, the stable unit treatment value assumption (SUTVA) is violated, and comparison of treatment and control outcomes may provide a biased assessment of the treatment’s causal influence. Social scientists are increasingly interested in the substantive phenomena that lead to SUTVA violations, such as communication in advance of an election. Experimental designs that gauge SUTVA violations provide useful insights into the extent and influence of interpersonal communication. This article illustrates the value of one such design, a multilevel experiment in which treatments are randomly assigned to individuals and varying proportions of their neighbors. After describing the theoretical and statistical underpinnings of this design, we apply it to a large-scale voter-mobilization experiment conducted in Chicago during a special election in 2009 using social-pressure mailings that highlight individual electoral participation. We find some evidence of within-household spillovers but no evidence of spillovers across households. We conclude by discussing how multilevel designs might be employed in other substantive domains, such as the study of deterrence and policy diffusion.
    [Show full text]
  • Robust Score and Portmanteau Tests of Volatility Spillover Mike Aguilar, Jonathan B
    Journal of Econometrics 184 (2015) 37–61 Contents lists available at ScienceDirect Journal of Econometrics journal homepage: www.elsevier.com/locate/jeconom Robust score and portmanteau tests of volatility spillover Mike Aguilar, Jonathan B. Hill ∗ Department of Economics, University of North Carolina at Chapel Hill, United States article info a b s t r a c t Article history: This paper presents a variety of tests of volatility spillover that are robust to heavy tails generated by Received 27 March 2012 large errors or GARCH-type feedback. The tests are couched in a general conditional heteroskedasticity Received in revised form framework with idiosyncratic shocks that are only required to have a finite variance if they are 1 September 2014 independent. We negligibly trim test equations, or components of the equations, and construct heavy Accepted 1 September 2014 tail robust score and portmanteau statistics. Trimming is either simple based on an indicator function, or Available online 16 September 2014 smoothed. In particular, we develop the tail-trimmed sample correlation coefficient for robust inference, and prove that its Gaussian limit under the null hypothesis of no spillover has the same standardization JEL classification: C13 irrespective of tail thickness. Further, if spillover occurs within a specified horizon, our test statistics C20 obtain power of one asymptotically. We discuss the choice of trimming portion, including a smoothed C22 p-value over a window of extreme observations. A Monte Carlo study shows our tests provide significant improvements over extant GARCH-based tests of spillover, and we apply the tests to financial returns data. Keywords: Finally, based on ideas in Patton (2011) we construct a heavy tail robust forecast improvement statistic, Volatility spillover which allows us to demonstrate that our spillover test can be used as a model specification pre-test to Heavy tails Tail trimming improve volatility forecasting.
    [Show full text]
  • Place Based Interventions at Scale: the Direct and Spillover Effects of Policing and City Services on Crime
    WORKING PAPER · NO. 2019-40 Place Based Interventions at Scale: The Direct and Spillover Effects of Policing and City Services on Crime Christopher Blattman, Donald Green, Daniel Ortega, Santiago Tobón JANUARY 2019 1126 E. 59th St, Chicago, IL 60637 Main: 773.702.5599 bfi.uchicago.edu Place-based interventions at scale: The direct and spillover effects of policing and city services on crime∗ Christopher Blattman Donald Green Daniel Ortega Santiago Tobón† January 15, 2019 Abstract In 2016 the city of Bogotá doubled police patrols and intensified city services on high-crime streets. They did so based on a policy and criminological consensus that such place-based programs not only decrease crime, but also have positive spillovers to nearby streets. To test this, we worked with Bogotá to experiment on an unprecedented scale. They randomly assigned 1,919 streets to either 8 months of doubled police patrols, greater municipal services, both, or neither. Such scale brings econometric challenges. Spatial spillovers in dense networks introduce bias and complicate variance estimation through “fuzzy clustering.” But a design-based approach and randomization inference produce valid hypothesis tests in such settings. In contrast to the consensus, we find intensifying state presence in Bogotá had modest but imprecise direct effects and that such crime displaced nearby, especially property crimes. Confidence intervals suggest we can rule out total reductions in crime of more than 2–3% from the two policies. More promising, however, is suggestive evidence that more state presence led to an 5% fall in homicides and rape citywide. One interpretation is that state presence may more easily deter crimes of passion than calculation, and place-based interventions could be targeted against these incredibly costly and violent crimes.
    [Show full text]
  • The Spillover Effects of Top Income Inequality
    The Spillover Effects of Top Income Inequality∗ Jeffrey Clemensy Joshua D. Gottliebz David H´emousx Morten Olsen{ November 2016 - Preliminary Abstract Since the 1980s top income inequality within occupations as diverse as bankers, managers, doctors, lawyers and scientists has increased considerably. Such a broad pattern has led the literature to search for a common explanation. In this paper, however, we argue that increases in income inequality originating within a few oc- cupations can\spill over"into others creating broader changes in income inequality. In particular, we study an assignment model where generalists with heterogeneous income buy the services of doctors with heterogeneous ability. In equilibrium the highest earning generalists match with the highest quality doctors and increases in income inequality among the generalists feed directly into the income inequal- ity of doctors. We use data from the Decennial Census as well as the American Community Survey from 1980 to 2014 to test our theory. Specifically, we identify occupations for which our consumption-driven theory predicts spill-overs and oc- cupations for which it does not and show that patterns align with the predictions of our model. In particular, using a Bartik-style instrument, we show that an increase in general income inequality causes higher income inequality for doctors, dentists and real estate agents; and in fact accounts for most of the increase of inequality in these occupations. ∗Morten Olsen gratefully acknowledges the financial support of the European Commission under the Marie Curie Research Fellowship program (Grant Agreement PCIG11-GA-2012-321693) and the Spanish Ministry of Economy and Competitiveness (Project ref: ECO2012-38134).
    [Show full text]
  • Dependence-Robust Inference Using Resampled Statistics
    Dependence-Robust Inference Using Resampled Statistics∗ Michael P. Leung† August 26, 2021 Abstract. We develop inference procedures robust to general forms of weak dependence. The procedures utilize test statistics constructed by resam- pling in a manner that does not depend on the unknown correlation structure of the data. We prove that the statistics are asymptotically normal under the weak requirement that the target parameter can be consistently estimated at the parametric rate. This holds for regular estimators under many well-known forms of weak dependence and justifies the claim of dependence-robustness. We consider applications to settings with unknown or complicated forms of de- pendence, with various forms of network dependence as leading examples. We develop tests for both moment equalities and inequalities. JEL Codes: C12, C31 Keywords: resampling, dependent data, social networks, clustered standard errors arXiv:2002.02097v4 [econ.EM] 25 Aug 2021 ∗I thank the editor and referees for comments that improved the quality of the paper. I also thank Eric Auerbach, Vittorio Bassi, Jinyong Hahn, Roger Moon, Hashem Pesaran, Kevin Song, and seminar audiences at UC Davis, USC INET, the 2018 Econometric Society Winter Meetings, the 2018 Econometrics Summer Masterclass and Workshop at Warwick, and the NetSci2018 Satellite on Causal Inference and Design of Experiments. This research is supported by NSF Grant SES-1755100. †Department of Economics, University of Southern California. E-mail: [email protected]. 1 Michael P. Leung 1 Introduction This paper builds on randomized subsampling tests due to Song (2016) and proposes inference procedures for settings in which the dependence structure of the data is complex or unknown.
    [Show full text]
  • A Data-Driven Method for Reconstructing a Distribution from a Truncated Sample with an Application to Inferring Car-Sharing Demand
    A data-driven method for reconstructing a distribution from a truncated sample with an application to inferring car-sharing demand Evan Fields1, Carolina Osorio1,2, and Tianli Zhou2 1Massachusetts Institute of Technology Operations Research Center 2Massachusetts Institute of Technology Civil and Environmental Engineering August 8, 2018 Abstract This paper proposes a method to recover an unknown probability distribution given a censored or truncated sample from that distribution. The proposed method is a novel and conceptually simple detruncation method based on sampling the observed data accord- ing to weights learned by solving a simulation-based optimization problem; this method is especially appropriate in cases where little analytic information is available but the truncation process can be simulated. The proposed method is compared to the ubiqui- tous maximum likelihood (MLE) method in a variety of synthetic validation experiments where it is found that the proposed method performs slightly worse than perfectly specified MLE and competitively with slight misspecified MLE . The practical application of this method is then demonstrated via a pair of case studies in which the proposed detruncation method is used alongside a car-sharing service simulator to estimate demand for round trip car-sharing services in the Boston and New York metropolitan areas. 1 Introduction Car-sharing is a transportation service in which travelers use cars that they do not own; the vehicles are thus shared between users of the car-sharing service. In this work, we focus on round-trip station-based car-sharing, which is one of the most common types of car-sharing worldwide (Barth and Shaheen 2002).
    [Show full text]
  • Spillover Effects in Experimental Data
    Spillover Effects in Experimental Data Peter M. Aronow, Yale Dean Eckles, MIT Cyrus Samii, NYU Stephanie Zonszein, NYU Abstract We present current methods for estimating treatment effects and spillover effects under “interference”, a term which covers a broad class of situations in which a unit’s outcome depends not only on treatments received by that unit, but also on treatments received by other units. To the extent that units react to each other, interact, or otherwise transmit effects of treatments, valid inference requires that we account for such interference, which is a departure from the traditional assumption that units’ outcomes are affected only by their own treatment assignment. Interference and associated spillovers may be a nuisance or they may be of substantive interest to the researcher. In this chapter, we focus on interference in the context of randomized experiments. We review methods for when interference happens in a general network setting. We then consider the special case where interference is contained within a hierarchical structure. Finally, we discuss the relationship between interference and contagion. We use the interference R package and simulated data to illustrate key points. We consider efficient designs that allow for estimation of the treatment and spillover effects and discuss recent empirical studies that try to capture such effects. arXiv:2001.05444v1 [stat.AP] 15 Jan 2020 1 1 Introduction We present current methods for identifying causal effects under “interference”, a term which covers a very broad class of situations in which a unit’s outcomes depend not only on treatments received by that unit, but also on treatments received by other units (Cox, 1958).
    [Show full text]
  • Treatment and Spillover Effects Under Network Interference
    Treatment and Spillover Effects under Network Interference Michael P. Leung˚ July 3, 2016 Abstract. We study identification and estimation of treatment and spillover effects when interference is mediated by a network, focusing on the case of ran- domized assignment. We show that identification of spillover effects is possible with only a single, possibly sampled, network under common shape restrictions on treatment response. Estimation in the single-network setting is nonstan- dard due to correlation between outcomes induced by network spillovers and correlated effects. Nonetheless, under restrictions on moments of the network, nonparametric estimators for treatment and spillover effects are consistent and asymptotically normal, and we can construct consistent variance estimators. We also derive analogous results for GMM estimators, including robust stan- dard errors. JEL Codes: C13, C21 Keywords: social networks, treatment effects, spillovers, SUTVA, Stein’s method ˚USC, Department of Economics and MIT, Institute for Data, Systems, and Society. E-mail: [email protected]. 1 Michael P. Leung 1 Introduction A vast literature in econometrics and statistics studies identification and estimation of treatment effects. In this literature, the stable-unit treatment value assumption (SUTVA) is a fundamental assumption, which states that the ego’s treatment response is invariant to the treatment assignment of any alter. In other words, there is no “interference” or are no “spillovers” in treatment assignment. However, there are many important contexts in which this assumption fails to hold, and the measurement of spillover effects is often of inherent interest. This paper studies identification and estimation of treatment and spillover effects in the absence of SUTVA. In our model, treatment response may depend on the treat- ment assignment of others in a network.
    [Show full text]
  • Identification and Estimation of Spillover Effects in Randomized
    Identification and Estimation of Spillover Effects in Randomized Experiments∗ Gonzalo Vazquez-Bare† June 17, 2021 Abstract I study identification, estimation and inference for spillover effects in experiments where units' outcomes may depend on the treatment assignments of other units within a group. I show that the commonly-used reduced-form linear-in-means (RF-LIM) regression identifies a weighted sum of spillover effects with some negative weights, and that the difference in means between treated and controls identifies a combination of direct and spillover effects entering with different signs. I propose nonparametric estimators for average direct and spillover effects that overcome these issues and are consistent and asymptotically normal under a precise relationship between the number of parameters of interest, the total sample size and the treatment assignment mechanism. These findings are illustrated using data from a conditional cash transfer program and with simulations. The empirical results reveal the potential pitfalls of failing to flexibly account for spillover effects in policy evaluation: the estimated difference in means and the RF-LIM coefficients are all close to zero and statistically insignificant, whereas the nonparametric estimators I propose reveal large, nonlinear and significant spillover effects. (JEL C10, C13, C14, C90) arXiv:1711.02745v7 [econ.EM] 15 Jun 2021 ∗I am deeply grateful to Matias Cattaneo for continued advice and support. I am indebted to Lutz Kilian, Mel Stephens and Roc´ıoTitiunik for thoughtful feedback and discussions that greatly improved the paper. I thank Cl´ement de Chaisemartin, Catalina Franco, Amelia Hawkins, Nicol´asIdrobo, Xinwei Ma, Nicolas Morales, Kenichi Nagasawa, Olga Namen and Doug Steigerwald for valuable discussions and suggestions.
    [Show full text]
  • Identification of Spillover Effects Using Panel Data
    Identification of Spillover Effects using Panel Data Christiern Rose∗ University of Queensland [email protected] Latest version: March 2018. First version: June 2013 Abstract In this paper I use panel data to identify and estimate spillover effects when the underlying network is sparse and unobserved. The outcome of each entity depends on its own covariates, the outcomes of others (endogenous effects), the covariates of others (contextual effects) and an entity-specific fixed effect. Sparsity restrictions are exclusion restrictions of unknown location, and lead to point identification if the network is suitably connected. Prior knowledge that a particular covariate does not generate contextual effects may also lead to point identification. I use the results of Gautier and Tsybakov(2014) for estimation, model selection and inference under sparsity. The results of a Monte Carlo experiment demonstrate applicability in realistic settings. I apply the approach to study R&D spillovers in an oligopoly model, finding that spillovers are sent predominantly by large firms and that R&D stocks are below the social optimum. My results do not depend on pre-specified competition and technology networks. JEL codes: C31, L14, L24 Key words: Networks, spillovers, panel data, peer effects, R&D spillovers, high-dimensional econometrics 1. Introduction Spillover effects occur in many applied settings, including technology adoption, treatment effects, risky behaviors, peer effects in education, economic growth, labor market performance and almost all strategic contexts. There are two types of spillover: endogenous effects, through which the outcomes of interest are simultaneously determined, and contextual effects, through which the outcomes depend on the covariates of others (Manski, 1993).
    [Show full text]
  • Spillover Effects in the Presence of Unobserved Networks
    Spillover Effects in the Presence of Unobserved Networks Naoki Egami Department of Political Science, Columbia University, New York, NY 10027, USA. Email: [email protected], URL: https://naokiegami.com https://doi.org/10.1017/pan.2020.28 . Abstract When experimental subjects can interact with each other, the outcome of one individual may be affected by the treatment status of others. In many social science experiments, such spillover effects may occur through multiple networks, for example, through both online and offline face-to-face networks in a Twit- ter experiment. Thus, to understand how people use different networks, it is essential to estimate the spillover effect in each specific network separately. However, the unbiased estimation of these network- specific spillover effects requires an oen-violated assumption that researchers observe all relevant networks. We show that, unlike conventional omitted variable bias, bias due to unobserved networks remains even when treatment assignment is randomized and when unobserved networks and a network of interest are https://www.cambridge.org/core/terms independently generated. We then develop parametric and nonparametric sensitivity analysis methods, with which researchers can assess the potential influence of unobserved networks on causal findings. We illustrate the proposed methods with a simulation study based on a real-world Twitter network and an empirical application based on a network field experiment in China. Keywords: causal inference, interference, potential outcomes, SUTVA, network experiments 1 Introduction Existing methodologies for causal inference oen assume the absence of spillover effects, that is, people are affected only by treatments directly assigned to them and not by those assigned to oth- ers (Cox 1958; Rubin 1980).
    [Show full text]
  • Handling Spillover Effects in Empirical Research: an Application Using
    Handling Spillover Effects in Empirical Research: An Application using Credit Supply Shocks ∗ Tobias Berg† Daniel Streitz‡§ This version: August 28, 2019 Abstract Despite their importance, the discussion of spillover effects in empirical research misses the rigor dedicated to endogeneity concerns. We show that i) even with random treatment, spillovers lead to an intricate bias in estimating treatment effects, ii) there is a trade-off between endogeneity and spillover concerns, iii) the practice of using individual level regressions to identify direct effects and aggregate level regressions to learn about spillover effects can lead to misleading conclusions. We develop a simple guidance for empirical researchers, apply it to a credit supply shock, and highlight differences in the results compared to current empirical practice. Keywords: Spillovers, Credit Supply, Direct vs. Indirect Effects, Aggregate Effects JEL: C13, C21, G21, G32, R11, R23 ∗We would like to thank Bo Bian (discussant), Benjamin Born, Falko Fecht, Emilia Garcia-Appendini, Thomas Geelen, Paul Goldsmith-Pinkham (discussant), Rainer Haselmann, Katharina Hombach, Kilian Huber (discussant), Michael Koetter, Thorsten Martin, John Mondragon (discussant), Karsten M¨uller, William Mullins, Steven Ongena, Clemens Otto, Lasse Petersen, Markus Reisinger, Zacharias Sautner, Larissa Sch¨afer,Oliver Schenker, Sascha Steffen, conference participants at the 2019 SFS Cavalcade in Pittsburgh, the 2019 FIRS Conference in Savannah, the 8th MoFiR Workshop on Banking, the 2019 Conference on Regulating Financial Markets in Frankfurt, as well as seminar participants at Copenhagen Business School, Frankfurt School of Finance and Management, Humboldt University of Berlin, IWH Halle, Maastricht University, and the University of Zurich for helpful comments and suggestions. Rafael Zincke provided excellent research assistance.
    [Show full text]