Knowledge that Transforms

In this paper I revisit the interpretation of the linear instrumental variables (IV) estimand as a weighted average of conditional local average treatment effects (LATEs). I focus on a situation in which additional covariates are required for identification while the reduced-form and first-stage regressions may be misspecified due to an implicit homogeneity restriction on the effects of the instrument. I show that the weights on some conditional LATEs are negative and the IV estimand is no longer interpretable as a causal effect under a weaker version of monotonicity, i.e. when there are compliers but no defiers at some covariate values and defiers but no compliers elsewhere. The problem of negative weights disappears in the interacted specification of Angrist and Imbens (I1995), which avoids misspecification and seems to be underused in applied work. I illustrate my findings in an application to the causal effects of pretrial detention on case outcomes. In this setting, I reject the stronger version of monotonicity, demonstrate that the interacted instruments are sufficiently strong for consistent estimation using the jackknife methodology, and present several estimates that are economically and statistically different, depending on whether the interacted instruments are used.

We study how online job search advice affects job search behavior and labor market outcomes of unemployed workers. In a large-scale field experiment embedded in the online platform of the Danish public employment service, we provide job seekers with vacancy information and occupational recommendations. Using a two-stage randomized design with regionally varying treatment intensities, we examine both direct effects of advice and treatment spillovers. We find that advice significantly increases employment and earnings when provided to a limited share of job seekers. As treatment intensity rises, these effects diminish and eventually disappear. The decline is driven by negative spillovers among treated job seekers, consistent with increased congestion in the occupations toward which job seekers redirect their search. Spillover effects on untreated job seekers are heterogeneous and depend on how advice alters occupation-specific competition in local labor markets.

Quality regulation seeks to ensure quality and foster competition by reducing vertical differentiation, but it may also have adverse effects on market structure. We study this trade-off in the context of pharmaceutical bioequivalence, which is the primary quality standard for generic drugs. By exploiting the introduction of bioequivalence in Chile, we find that stronger regulation reduced the number of drugs in the market by 18% and increased average paid prices by 13%. We estimate a model of drug entry, certification, and demand to study how drug quality, aversion to generics, and certification costs shape the equilibrium effects of quality regulation. We find that quality regulation increased demand for generic drugs by resolving asymmetric information and reducing aversion to unbranded generics, which induced the entry of high-quality drugs in place of low-quality drugs. Consumer welfare increased despite higher prices and a lower number of firms. We compare minimum quality standards with alternative designs of quality regulation, including quality disclosure.

When financial constraints bind, firms adjust employment in response to cash flow shocks. A 2010 revaluation of business rates, a UK tax levied on business-occupied properties, implied that similar firms, occupying similar properties in narrow geographical locations, experienced different tax changes. I find that, on average, for every ￡1 of additional cash flow triggered by the tax change, 39 pence were spent on employment, with small and leveraged firms responding the most. I use these findings to discipline a general equilibrium model with firm heterogeneity and financial frictions and quantitatively determine the aggregate effects of a fiscal transfer to firms.

We compare and combine two distinct approaches to estimating market power in the US brewing industry—one based on production data, the other on demand. Both methods produce similar estimates of average markups and reveal a recent upward trend. We then combine the two approaches in two ways. First, we replace conventional instruments in demand estimation with a moment involving a production-based markup estimate, yielding similar results. We then evaluate the common (but controversial) assumption that retail markets operate competitively, finding that demand-based markups recovered with the assumption of competitive retail markets align with production-based estimates, as long as downstream costs are accounted for.

Even as global oil demand has increased in recent years, it is plausible to envision scenarios in which clean energy technologies or climate policies drive demand to essentially zero by the century’s end. This paper asks what such a demand decline, when anticipated, might mean for global oil supply. One possibility is a “green paradox”: producers accelerate extraction. However, because extraction requires durable capital investments, the opposite may occur: producers reduce their investment rate, decreasing extraction. To evaluate the relative strengths of these opposing mechanisms, I develop a model of global oil supply that incorporates both, among other industry features. For model inputs with the strongest empirical support, both effects are modest, with disinvestment typically outweighing the green paradox. In order for the green paradox to substantially increase cumulative global oil extraction, investments must have short time horizons, and producers’ discount rates must be less than 4% real.

We use a sufficient statistic approach to quantify the general equilibrium effects of population aging on the returns to wealth, wealth accumulation, and global imbalances. Combining population forecasts with household survey data from 25 countries, we measure the compositional effect of aging: how a changing age distribution affects wealth-to-GDP, holding the age profiles of wealth and labor income fixed. In a baseline overlapping generations model this statistic, in conjunction with cross-sectional information and two standard macro parameters, pins down general equilibrium outcomes. Since the compositional effect is positive, large, and heterogeneous across countries, our model predicts that population aging will lower returns to wealth, increase wealth-to-GDP ratios, and widen global imbalances through the twenty-first century. These conclusions extend to a richer model in which bequests, individual savings, and the tax-and-transfer system all respond to demographic change.

Market definition is challenging in settings with network effects, where substitution patterns depend on changes in network size. We study these effects in the context of social media. We conduct an incentivized experiment comparing substitution in response to a proposed U.S. TikTok ban, in which all users simultaneously leave the app, with substitution when only a single user deactivates. We find substantially higher valuations of alternative social apps under a collective TikTok ban than under an individual TikTok deactivation. Mechanism evidence shows that both anticipated content-supply shifts and social coordination partly explain the wedge, with the relative importance of each channel varying across platforms. We then show that a collective time limit challenge, where peers jointly reduce TikTok and Instagram use, leads to more time spent on alternative social apps than has been observed in prior individual deactivation experiments. Together, our results suggest that individual-level substitution estimates can be an unreliable guide to market definition for network goods.

We study how supply disruptions interact with monopoly pricing, inventory management, and consumer stockpiling in a continuous-time model. Preemption incentives—consumers prefer to stock up before a price hike while the firm prefers to hike before consumers stock up—lead to an equilibrium with gradual stockpiling and endogenous uncertainty over the timing of a price hike, which can trigger a run at the disruption onset. Consumer storage introduces welfare losses from randomized pricing, but can also strengthen the firm’s incentive to hold buffer stock. Rationing, price controls, and reserve mandates can each improve welfare, but only strategic government reserves can implement the social optimum.

Do workers from social groups with comparable productivity distributions obtain comparable lifetime earnings? We study how a small amount of early-career discrimination propagates over time when workers’ productivity is revealed through employment. In breakdown learning environments that primarily track on-the-job failures, such discrimination spirals into a substantial lifetime earnings gap for groups of comparable productivity, whereas in breakthrough learning environments that track successes, early-career discrimination can be self-corrected, so comparable groups obtain comparable lifetime earnings. This contrast persists in large labor markets and with flexible wages, inconclusive learning, and misspecified employer beliefs.