Semiparametric Sensitivity Analysis: Unmeasured Confounding In Observational Studies

Establishing cause-effect relationships from observational data often relies on untestable assumptions. It is crucial to know whether, and to what extent, the conclusions drawn from non-experimental studies are robust to potential unmeasured confounding. In this paper, we focus on the average causal effect (ACE) as our target of inference. We generalize the sensitivity analysis approach developed by Robins et al. (2000), Franks et al. (2020) and Zhou and Yao (2023. We use semiparametric theory to derive the non-parametric efficient influence function of the ACE, for fixed sensitivity parameters. We use this influence function to construct a one-step bias-corrected estimator of the ACE. Our estimator depends on semiparametric models for the distribution of the observed data; importantly, these models do not impose any restrictions on the values of sensitivity analysis parameters. We establish sufficient conditions ensuring that our estimator has root-n asymptotics. We use our methodology to evaluate the causal effect of smoking during pregnancy on birth weight. We also evaluate the performance of estimation procedure in a simulation study

Midterm results on a new self-expandable covered stent combined with branched stent grafts: Insights from a multicenter Italian registry

Objective: To investigate the technical periprocedural and midterm outcomes of endovascular repairs with multibranched endovascular repair or iliac branch devices combined with a new self-expanding covered stent. Methods: The COvera in BRAnch registry is a physician-initiated, multicenter, ambispective, observational registry (ClinicalTrials.gov Identifier: NCT04598802) enrolling patients receiving a multibranched endovascular repair or iliac branch devices procedure mated with Bard Covera Plus (Tempe, AZ) covered stent, designed to evaluate the outcomes of the covered stent mated with patient-specific and off-the-shelf branched stent graft. Primary end points were technical success, branch instability, and freedom from aortic and branch-related reintervention within 30 days and at follow-up. Preoperative characteristics, comorbidities, and outcomes definitions were graded according to the Society for Vascular Surgery reporting standards. Results: Two hundred eighty-four patients (76 years; range, 70-80 years; 79% males) in 24 centers were enrolled for a total of 708 target vessels treated. The covered stents were mated with an off-the-shelf graft in 556 vessels (79%) and a custom-made graft in 152 (21%). Three hundred seven adjunctive relining stents in 277 vessels (39%) were deployed, of which 116 (38%) were proximal, 66 (21%) intrastent, and 125 (41%) distal. Adjunctive relining stent placement was more frequent when landing in a vessel branch instead of the main trunk (59% vs 39%; P = .031), performing a percutaneous access (49% vs 35%; P < .001), using a stent with a diameter of 8 mm or greater (44% vs 36%; P = .032) and a length of 80 mm or greater (65% vs 55%; P = .005), when a post-dilatation was not performed (45% vs 29%; P < .001) and when an inner branch configuration was used (55% vs 35%; P < .001). Perioperative technical bridging success was 98%. Eight patients (3%) died in the perioperative period. Two deaths (1%) were associated with renal branch occlusion followed by acute kidney injury and paraplegia. Follow-up data were available for 638 vessels (90%) at a median of 32 months (Q1, Q3, 21, 46). Branch instability was reported in 1% of branches. Forty-six patients (17%) died during follow-up, nine (3%) of them owing to aortic-related causes. Primary patency rates at 1, 2, and 3 years were 99% (581/587), 99% (404/411), and 97% (272/279), respectively. Branch instability was associated with patient-specific devices (9% vs 4%; P = .014) and intrastent adjunctive stent placement (12% vs 2%; P = .003), especially when a bare metal balloon-expandable stent was used (25% vs 3%; P < .001). Conclusions: The use of this new self-expanding covered stent mated with branched endografts proved to be safe and feasible with high technical procedural success rates. Low rates of branch instability were observed at midterm follow-up. Comparative studies with other commercially available covered stents are warranted

Top-pair production at hadron colliders with next-to-next-to-leading logarithmic soft-gluon resummation

Incorporating all recent theoretical advances, we resum soft-gluon corrections to the total $t\bar t$ cross-section at hadron colliders at the next-to-next-to-leading logarithmic (NNLL) order. We perform the resummation in the well established framework of Mellin $N$-space resummation. We exhaustively study the sources of systematic uncertainty like renormalization and factorization scale variation, power suppressed effects and missing two- and higher-loop corrections. The inclusion of soft-gluon resummation at NNLL brings only a minor decrease in the perturbative uncertainty with respect to the NLL approximation, and a small shift in the central value, consistent with the quoted uncertainties. These numerical predictions agree with the currently available measurements from the Tevatron and LHC and have uncertainty of similar size. We conclude that significant improvements in the $t\bar t$ cross-sections can potentially be expected only upon inclusion of the complete NNLO corrections.Comment: 17 pages, 4 figures. V2 updates tables and figures including results for sqrt(S)=8 TeV. Version to appear in Phys Lett

The forward physics facility at the high-luminosity LHC

High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe standard model (SM) processes and search for physics beyond the standard model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential

Patterns of care for anal cancer in the United States - a comparison between academic and community cancer centers

Abstract Background Management of squamous cell carcinoma of the anus (SCCA) is becoming more relevant, as its incidence increases. The purpose of this study was to investigate possible differences in patient population and care delivery for SCCA between academic and community cancer programs in the United States. Methods A review of available data from the American College of Surgeons Committee on Cancer National Cancer DataBase focused on gender, age, race, type of health insurance, comorbidity score, distance traveled for care, stage at diagnosis, and therapy utilization (surgery, chemotherapy, and radiation therapy) as first course of treatment (FCT). The analysis included 38,766 patients treated for SCCA. Of them, 14,422 patients received treatment at Academic Cancer Programs (ACPs), while 24,344 were treated at Community Cancer Programs (CCPs) between the years 2003 and 2013. Results Over the 11-year study period, ACPs had significantly more male patients, of younger age, a greater non-white race population, with more Medicaid or no insurance coverage, who traveled farther for cancer center care (p < 0.001). There was no difference between ACPs and CCPs with respect to Charlson co-morbidity score and stage of SCCA at diagnosis. For stage 0 patients, use of chemotherapy was 8% for ACPs, 9% for CCPs, and use of radiotherapy was 10% for ACPs and 14% for CCPs. The incidence of stage unknown was identical at both ACPs and CCPs (11.5%). CCPs had a greater overall utilization of radiation therapy as FCT for stage 0, I, II and IV patients (p < 0.001). Conclusions Our study indicates that gender, demographic and socio-economic differences exist in the patient population with SCCA accessing different cancer programs in the US. The high incidence of stage unknown patients reflects ongoing challenges in the pre-treatment phase. A significant percentage of stage 0 patients received systemic chemotherapy and/or radiotherapy, rather than surgery alone. Despite comparable stage at diagnosis and comorbidity scores between ACPs and CCPs, there appear to be variations in treatment choices, especially with the use of radiotherapy, with associated cost and toxicity risks. Further analysis and monitoring of SCCA management in the US may lead to improved compliance with NCCN guidelines

Covariate-assisted bounds on causal effects with instrumental variables

When an exposure of interest is confounded by unmeasured factors, an instrumental variable (IV) can be used to identify and estimate certain causal contrasts. Identification of the marginal average treatment effect (ATE) from IVs relies on strong untestable structural assumptions. When one is unwilling to assert such structure, IVs can nonetheless be used to construct bounds on the ATE. Famously, Balke and Pearl (1997) proved tight bounds on the ATE for a binary outcome, in a randomized trial with noncompliance and no covariate information. We demonstrate how these bounds remain useful in observational settings with baseline confounders of the IV, as well as randomized trials with measured baseline covariates. The resulting bounds on the ATE are non-smooth functionals, and thus standard nonparametric efficiency theory is not immediately applicable. To remedy this, we propose (1) under a novel margin condition, influence function-based estimators of the bounds that can attain parametric convergence rates when the nuisance functions are modeled flexibly, and (2) estimators of smooth approximations of these bounds. We propose extensions to continuous outcomes, explore finite sample properties in simulations, and illustrate the proposed estimators in a randomized field experiment studying the effects of canvassing on resulting voter turnout.Comment: 40 pages, 2 figure