Many empirical studies leverage shift-share (or "Bartik") instruments that average a set of observed shocks with shock exposure weights. We derive a necessary and sufficient shock-level orthogonality condition for these instruments to identify causal effects. We then show that orthogonality holds when observed shocks are as-good-as-randomly assigned and growing in number, with the average shock exposure sufficiently dispersed. Quasiexperimental shift-share designs may be implemented with new shock-level procedures, which help visualize the identifying variation, correct standard errors, choose appropriate specifications, test identifying assumptions, and optimally combine multiple sets of quasi-random shocks. We illustrate these ideas by revisiting Autor et al. (2013)'s analysis of the labor market effects of Chinese import competition.

Summary Background Reoperation rates are high after surgery for hip fractures. We investigated the effect of a sliding hip screw versus cancellous screws on the risk of reoperation and other key outcomes. Methods For this international, multicentre, allocation concealed randomised controlled trial, we enrolled patients aged 50 years or older with a low-energy hip fracture requiring fracture fixation from 81 clinical centres in eight countries. Patients were assigned by minimisation with a centralised computer system to receive a single large-diameter screw with a side-plate (sliding hip screw) or the present standard of care, multiple small-diameter cancellous screws. Surgeons and patients were not blinded but the data analyst, while doing the analyses, remained blinded to treatment groups. The primary outcome was hip reoperation within 24 months after initial surgery to promote fracture healing, relieve pain, treat infection, or improve function. Analyses followed the intention-to-treat principle. This study was registered with ClinicalTrials.gov, number NCT00761813. Findings Between March 3, 2008, and March 31, 2014, we randomly assigned 1108 patients to receive a sliding hip screw (n=557) or cancellous screws (n=551). Reoperations within 24 months did not differ by type of surgical fixation in those included in the primary analysis: 107 (20%) of 542 patients in the sliding hip screw group versus 117 (22%) of 537 patients in the cancellous screws group (hazard ratio [HR] 0.83, 95% CI 0.63–1.09; p=0.18). Avascular necrosis was more common in the sliding hip screw group than in the cancellous screws group (50 patients [9%] vs 28 patients [5%]; HR 1.91, 1.06–3.44; p=0.0319). However, no significant difference was found between the number of medically related adverse events between groups (p=0.82; appendix); these events included pulmonary embolism (two patients [<1%] vs four [1%] patients; p=0.41) and sepsis (seven [1%] vs six [1%]; p=0.79). Interpretation In terms of reoperation rates the sliding hip screw shows no advantage, but some groups of patients (smokers and those with displaced or base of neck fractures) might do better with a sliding hip screw than with cancellous screws. Funding National Institutes of Health, Canadian Institutes of Health Research, Stichting NutsOhra, Netherlands Organisation for Health Research and Development, Physicians’ Services Incorporated.

Following surgery to treat major trauma-related fractures, deep wound infection rates are high. It is not known if negative pressure wound therapy can reduce infection rates in this setting. OBJECTIVE To assess outcomes in patients who have incisions resulting from surgery for lower limb fractures related to major trauma and were treated with either incisional negative pressure wound therapy or standard wound dressing. DESIGN, SETTING, AND PARTICIPANTS A randomized clinical trial conducted at 24 trauma hospitals representing the UK Major Trauma Network that included 1548 patients aged 16 years or older who underwent surgery for a lower limb fracture caused by major trauma from

Many studies use shift-share (or “Bartik”) instruments, which average a set of shocks with exposure share weights. We provide a new econometric framework for shift-share instrumental variable (SSIV) regressions in which identification follows from the quasi-random assignment of shocks, while exposure shares are allowed to be endogenous. The framework is motivated by an equivalence result: the orthogonality between a shift-share instrument and an unobserved residual can be represented as the orthogonality between the underlying shocks and a shock-level unobservable. SSIV regression coefficients can similarly be obtained from an equivalent shock-level regression, motivating shock-level conditions for their consistency. We discuss and illustrate several practical insights of this framework in the setting of Autor et al. (2013), estimating the effect of Chinese import competition on manufacturing employment across U.S. commuting zones.

Conventional value-added models (VAMs) compare average test scores across schools after regression-adjusting for students’ demographic characteristics and previous scores. This article tests for VAM bias using a procedure that asks whether VAM estimates accurately predict the achievement consequences of random assignment to specific schools. Test results from admissions lotteries in Boston suggest conventional VAM estimates are biased, a finding that motivates the development of a hierarchical model describing the joint distribution of school value-added, bias, and lottery compliance. We use this model to assess the substantive importance of bias in conventional VAM estimates and to construct hybrid value-added estimates that optimally combine ordinary least squares and lottery-based estimates of VAM parameters. The hybrid estimation strategy provides a general recipe for combining nonexperimental and quasi-experimental estimates. While still biased, hybrid school value-added estimates have lower mean squared error than conventional VAM estimates. Simulations calibrated to the Boston data show that, bias notwithstanding, policy decisions based on conventional VAMs that control for lagged achievement are likely to generate substantial achievement gains. Hybrid estimates that incorporate lotteries yield further gains.

Purpose; The COVID-19 pandemic has necessitated profound adaptations in the delivery of healthcare to manage a rise in critically unwell patients. In an attempt to slow the spread of the virus nationwide lockdown restrictions were introduced. This review aims to scope the literature on the impact of the pandemic and subsequent lockdown on the presentation and management of trauma globally. Methods; A scoping review was conducted in accordance with PRISMA-ScR guidelines. A systematic search was carried out on the Medline, EMBASE and Cochrane databases to identify papers investigating presentation and management of trauma during the COVID-19 pandemic. All studies based on patients admitted with orthopaedic trauma during the COVID-19 pandemic were included. Exclusion criteria were opinion-based reports, reviews, studies that did not provide quantitative data and papers not in English. Results; Three hundred and thirty seven studies were screened, with 17 meeting the eligibility criteria. Studies reported on the footfall of trauma in the UK, Europe, Asia, USA, Australia and New Zealand. A total of 29,591 patients during the pandemic were considered. Mean age was 43.7 years (range <1–103); 54.8% were male. Reported reductions in trauma footfall ranged from 20.3% to 84.6%, with a higher proportion of trauma occurring secondary to interpersonal violence, deliberate self-harm and falls from a height. A decrease was seen in road traffic collisions, sports injuries and trauma occurring outdoors. There was no significant change in the proportion of patients managed operatively, and the number of trauma patients reported to be COVID-19 positive was low. Conclusion; Whilst the worldwide COVID-19 pandemic has caused a reduction in the number of trauma patients; the services managing trauma have continued to function despite infrastructural, personnel and pathway changes in health systems. The substantial effect of the COVID-19 pandemic on elective orthopaedics is well described, however the contents of this review evidence minimal change in the delivery of effective trauma care despite resource constraints during this global COVID-19 pandemic.

Workshop on Quantitative Research Methods for suggestions and comments. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research. Angrist's daughter teaches at a Boston charter school. NBER working papers are circulated for discussion and comment purposes. They have not been peer-reviewed or been subject to the review by the NBER Board of Directors that accompanies official NBER publications.

OCA assumes liability for its contents or use thereof.NBER working papers are circulated for discussion and comment purposes. They have not been peer-reviewed or been subject to the review by the NBER Board of Directors that accompanies official NBER publications.