Abstract：African agricultural markets are characterized by low farmer revenues and high consumer food prices. Many have worried that this wedge is partially driven by imperfect competition among intermediaries. This paper provides experimental evidence from Kenya on intermediary market structure. Randomized cost shocks and demand subsidies are used to identify a structural model of market competition. Estimates reveal that traders act consistently with joint profit maximization and earn median markups of 39 percent. Exogenously induced firm entry has negligible effects on prices, and low take-up of subsidized entry offers implies large fixed costs. We estimate that traders capture 82 percent of total surplus.
参考文献：Bergquist, Lauren Falcao, and Michael Dinerstein. 2020. "Competition and Entry in Agricultural Markets: Experimental Evidence from Kenya." American Economic Review, 110 (12): 3705-47.
Abstract：We present a new equilibrium search model where consumers initially search among discount opportunities, but are willing to pay more as a deadline approaches, eventually turning to full-price sellers. The model predicts equilibrium price dispersion and rationalizes discount and full-price sellers coexisting without relying on ex ante heterogeneity. We apply the model to online retail sales via auctions and posted prices, where failed attempts to purchase reveal consumers' reservation prices. We find robust evidence supporting the theory. We quantify dynamic search frictions arising from deadlines and show how, with deadline-constrained buyers, seemingly neutral platform fee increases can cause large market shifts.
参考文献：Coey, Dominic, Bradley J. Larsen, and Brennan C. Platt. 2020. "Discounts and Deadlines in Consumer Search." American Economic Review, 110 (12): 3748-85.
Abstract：We formalize the argument that political disagreements can be traced to a "clash of narratives." Drawing on the "Bayesian Networks" literature, we represent a narrative by a causal model that maps actions into consequences, weaving a selection of other random variables into the story. Narratives generate beliefs by interpreting long-run correlations between these variables. An equilibrium is defined as a probability distribution over narrative-policy pairs that maximize a representative agent's anticipatory utility, capturing the idea that people are drawn to hopeful narratives. Our equilibrium analysis sheds light on the structure of prevailing narratives, the variables they involve, the policies they sustain, and their contribution to political polarization.
参考文献：Eliaz, Kfir, and Ran Spiegler. 2020. "A Model of Competing Narratives." American Economic Review, 110 (12): 3786-3816.
Abstract：We study anonymous repeated games where players may be "commitment types" who always take the same action. We establish a stark anti-folk theorem: if the distribution of the number of commitment types satisfies a smoothness condition and the game has a "pairwise dominant" action, this action is almost always taken. This implies that cooperation is impossible in the repeated prisoner's dilemma with anonymous random matching. We also bound equilibrium payoffs for general games. Our bound implies that industry profits converge to zero in linear-demand Cournot oligopoly as the number of firms increases.
参考文献：Sugaya, Takuo, and Alexander Wolitzky. 2020. "A Few Bad Apples Spoil the Barrel: An Anti-folk Theorem for Anonymous Repeated Games with Incomplete Information." American Economic Review, 110 (12): 3817-35.
Abstract：We analyze selection into screening in the context of recommendations that breast cancer screening start at age 40. Combining medical claims with a clinical oncology model, we document that compliers with the recommendation are less likely to have cancer than younger women who select into screening or women who never screen. We show this selection is quantitatively important: shifting the recommendation from age 40 to 45 results in three times as many deaths if compliers were randomly selected than under the estimated patterns of selection. The results highlight the importance of considering characteristics of compliers when making and designing recommendations.
参考文献：Einav, Liran, Amy Finkelstein, Tamar Oostrom, Abigail Ostriker, and Heidi Williams. 2020. "Screening and Selection: The Case of Mammograms." American Economic Review, 110 (12): 3836-70.
Abstract：Macroeconomic news announcements are elaborate and multi-dimensional. We consider a framework in which jumps in asset prices around announcements reflect both the response to observed surprises in headline numbers and to latent factors, reflecting other news in the release. Non-headline news, for which there are no expectations surveys, is unobservable to the econometrician but nonetheless elicits a market response. We estimate the model by the Kalman filter, which efficiently combines OLS and heteroskedasticity-based event study estimators in one step. With the inclusion of a single latent surprise factor, essentially all yield curve variance in event windows are explained by news.
参考文献：Gürkaynak, Refet S., Burçin Kisacikoğlu, and Jonathan H. Wright. 2020. "Missing Events in Event Studies: Identifying the Effects of Partially Measured News Surprises." American Economic Review, 110 (12): 3871-3912.
Abstract：We study the complexity of rules by paying experimental subjects to implement a series of algorithms and then eliciting their willingness-to-pay to avoid implementing them again in the future. The design allows us to examine hypotheses from the theoretical "automata" literature about the characteristics of rules that generate complexity costs. We find substantial aversion to complexity and a number of regularities in the characteristics of rules that make them complex and costly for subjects. Experience with a rule, the way a rule is represented, and the context in which a rule is implemented (mentally versus physically) also influence complexity.
参考文献：Oprea, Ryan. 2020. "What Makes a Rule Complex?" American Economic Review, 110 (12): 3913-51.
Abstract：The pace of job reallocation has declined in the United States in recent decades. We draw insight from canonical models of business dynamics in which reallocation can decline due to (i) lower dispersion of idiosyncratic shocks faced by businesses, or (ii) weaker marginal responsiveness of businesses to shocks. We show that shock dispersion has actually risen, while the responsiveness of business-level employment to productivity has weakened. Moreover, declining responsiveness can account for a significant fraction of the decline in the pace of job reallocation, and we find suggestive evidence this has been a drag on aggregate productivity.
参考文献：Decker, Ryan A., John Haltiwanger, Ron S. Jarmin, and Javier Miranda. 2020. "Changing Business Dynamism and Productivity: Shocks versus Responsiveness." American Economic Review, 110 (12): 3952-90.
Abstract：Fang and Gong (2017) develop a procedure to detect potential overbilling of Medicare by physicians. In their empirical analysis, they use aggregated claims data that can overstate the number of services performed due to features of Medicare billing. In this comment, I show how auditors can use detailed claims-level data to better target improper overbilling.
参考文献：Matsumoto, Brett. 2020. "Detecting Potential Overbilling in Medicare Reimbursement via Hours Worked: Comment." American Economic Review, 110 (12): 3991-4003.
