Economics Journal Articles

Journal Article
Shepard, Mark, and Ethan Forsgren. Forthcoming. “Do Insurers Respond to Active Purchasing? Evidence from the Massachusetts Health Insurance Exchange.” Journal of Risk and Insurance. Abstract
As the ACA Marketplaces face continued challenges with high premiums and limited insurer competition, there is significant interest in how policymakers can stabilize markets and control costs. We describe a unique set of active purchasing policies used by Massachusetts’ health insurance exchange to shape the rules of competition and reward lower-price insurers with additional customers. In contrast to the typical focus on recruiting new insurers to an exchange, Massachusetts focused on shaping insurer incentives by creating a series of carrots and sticks for setting prices below certain thresholds or below other insurers’ prices. We provide evidence that insurer pricing was significantly influenced by active purchasing policies. Between 2010 and 2013, over 80% of insurer prices were set exactly at or within 1% of pricing thresholds created by active purchasing policies. One key “limited choice” policy—which restricted the choice set of fully-subsidized consumers to the two cheapest plans—was associated with a 16-20% reduction in average insurance prices relative to comparison insurance markets in 2012-2014. Insurers achieved these price cuts partly through cost reductions via narrower provider networks and partly through reduced profit margins. The state’s slower price growth continued during the ACA’s first years, with the Connector having among the lowest benchmark premiums of any state starting in 2017.
Paper (PDF)
Geruso, Michael, Timothy J. Layton, Grace McCormack, and Mark Shepard. Forthcoming. “The Two Margin Problem in Insurance Markets.” Review of Economics and Statistics. Abstract

Insurance markets often feature consumer sorting along both an extensive margin (whether to buy) and an intensive margin (which plan to buy). We present a new graphical theoretical framework that extends the workhorse model to incorporate both selection margins simultaneously. A key insight from our framework is that policies aimed at addressing one margin of selection often involve an economically meaningful trade-off on the other margin in terms of prices, enrollment, and welfare. For example, while a larger penalty for opting to remain uninsured reduces the uninsurance rate, it also tends to lead to unraveling of generous coverage because the newly insured are healthier and sort into less generous plans, driving down the relative prices of those plans. While risk adjustment transfers shift enrollment from lower- to higher-generosity plans, they also sometimes increase the uninsurance rate by raising the prices of less generous plans, which are the entry points into the market. We illustrate these trade-offs in an empirical sufficient statistics approach that is tightly linked to the graphical framework. Using data from Massachusetts, we show that in many policy environments these trade-offs can be empirically meaningful and can cause these policies to have unexpected consequences for overall social welfare.

ReStat Version (PDF) Final Working Paper

Health insurers increasingly compete on their networks of medical providers. Using data from Massachusetts’ insurance exchange, I find substantial adverse selection against plans covering the most prestigious and expensive “star” hospitals. I highlight a theoretically distinct selection channel: consumers loyal to star hospitals incur high spending, conditional on their medical state, because they use these hospitals' expensive care. This implies heterogeneity in consumers' incremental costs of gaining access to star hospitals, posing a challenge for standard selection policies. Along with selection on unobserved sickness, I find this creates strong incentives to exclude star hospitals, even with risk adjustment in place.


Final Paper (PDF) Presentation Slides
McIntyre, Adrianna, Mark Shepard, and Myles Wagner. 2021. “Can Automatic Retention Improve Health Insurance Market Outcomes?” American Economic Review, Papers & Proceedings 111: 560-66. Published Version Abstract
There is growing interest in market design using default rules and other "choice architecture” principles to steer consumers toward desirable outcomes. Using data from Massachusetts’ health insurance exchange, we study an “automatic retention” policy intended to prevent coverage interruptions among low-income enrollees. Rather than disenroll people who lapse in paying premiums, the policy automatically switches them to an available free plan until they actively cancel or lose eligibility. We find that automatic retention has a sizable impact, switching 14% of consumers annually and differentially retaining healthy, low-cost individuals. The results illustrate the power of defaults to shape insurance coverage outcomes.
Published Version (PDF) NBER Working Paper (PDF) Summary and Policy Brief (PDF)
Jaffe, Sonia, and Mark Shepard. 2020. “Price-Linked Subsidies and Imperfect Competition in Health Insurance.” American Economic Journal: Economic Policy 12 (3): 279-311. Published Version Abstract

Policymakers subsidizing health insurance often face uncertainty about future market prices. We study the implications of one policy response: linking subsidies to prices, to target a given post-subsidy premium. We show that these price-linked subsidies weaken competition, raising prices for the government and/or consumers. However, price-linking also ties subsidies to health care cost shocks, which may be desirable. Evaluating this tradeoff empirically using a model estimated with Massachusetts insurance exchange data, we find that price-linking increases prices 1-6%, and much more in less competitive markets. For cost uncertainty reasonable in a mature market, these losses outweigh the benefits of price-linking.

Paper Online Appendix
Finkelstein, Amy, Nathaniel Hendren, and Mark Shepard. 2019. “Subsidizing Health Insurance for Low-Income Adults: Evidence from Massachusetts.” American Economic Review 109 (4). Publisher's Version Abstract

How much are low-income individuals willing to pay for health insurance, and what are the implications for insurance markets? Using administrative data from Massachusetts’ subsidized insurance exchange, we exploit discontinuities in the subsidy schedule to estimate willingness to pay and costs of insurance among low-income adults. As subsidies decline, insurance take-up falls rapidly, dropping about 25% for each $40 increase in monthly enrollee premiums. Marginal enrollees tend to be lower-cost, consistent with adverse selection into insurance. But across the entire distribution we can observe – approximately the bottom 70% of the willingness to pay distribution – enrollee willingness to pay is always less than half of own expected costs. As a result, we estimate that take-up will be highly incomplete even with generous subsidies: if enrollee premiums were 25% of insurers’ average costs, at most half of potential enrollees would buy insurance; even premiums subsidized to 10% of average costs would still leave at least 20% uninsured. We suggest an important role for uncompensated care for the uninsured in explaining these findings and explore normative implications.

Paper Executive Summary Presentation Slides
Ho, Kate, Ariel Pakes, and Mark Shepard. 2018. “The Evolution of Health Insurer Costs in Massachusetts, 2010-12.” Review of Industrial Organization 53 (1): 117-137. NBER Working Paper #22835 Abstract

We analyze the evolution of health insurer costs in Massachusetts between 2010-2012, paying particular attention to changes in the composition of enrollees. This was a period in which Health Maintenance Organizations (HMOs) increasingly used physician cost control incentives but Preferred Provider Organizations (PPOs) did not. We show that cost growth and its components cannot be understood without accounting for (i) consumers’ switching between plans, and (ii) differences in cost characteristics between new entrants and those leaving the market. New entrants are markedly less costly than those leaving (and their costs fall after their entering year), so cost growth of continuous enrollees in a plan is significantly higher than average per-member cost growth. Relatively high-cost HMO members switch to PPOs while low-cost PPO members switch to HMOs, so the impact of cost control incentives on HMO costs is likely different from their impact on market-wide insurer costs.

Paper (PDF)