86 research outputs found
Comparing multiple competing interventions in the absence of randomized trials using clinical risk-benefit analysis
<p>Abstract</p> <p>Background</p> <p>To demonstrate the use of risk-benefit analysis for comparing multiple competing interventions in the absence of randomized trials, we applied this approach to the evaluation of five anticoagulants to prevent thrombosis in patients undergoing orthopedic surgery.</p> <p>Methods</p> <p>Using a cost-effectiveness approach from a clinical perspective (i.e. risk benefit analysis) we compared thromboprophylaxis with warfarin, low molecular weight heparin, unfractionated heparin, fondaparinux or ximelagatran in patients undergoing major orthopedic surgery, with sub-analyses according to surgery type. Proportions and variances of events defining risk (major bleeding) and benefit (thrombosis averted) were obtained through a meta-analysis and used to define beta distributions. Monte Carlo simulations were conducted and used to calculate incremental risks, benefits, and risk-benefit ratios. Finally, net clinical benefit was calculated for all replications across a range of risk-benefit acceptability thresholds, with a reference range obtained by estimating the case fatality rate - ratio of thrombosis to bleeding.</p> <p>Results</p> <p>The analysis showed that compared to placebo ximelagatran was superior to other options but final results were influenced by type of surgery, since ximelagatran was superior in total knee replacement but not in total hip replacement.</p> <p>Conclusions</p> <p>Using simulation and economic techniques we demonstrate a method that allows comparing multiple competing interventions in the absence of randomized trials with multiple arms by determining the option with the best risk-benefit profile. It can be helpful in clinical decision making since it incorporates risk, benefit, and personal risk acceptance.</p
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Current model capabilities for simulating black carbon and sulfate concentrations in the Arctic atmosphere: a multi-model evaluation using a comprehensive measurement data set
The concentrations of sulfate, black carbon (BC) and other aerosols in the Arctic are characterized by high values in late winter and spring (so-called Arctic Haze) and low values in summer. Models have long been struggling to capture this seasonality and especially the high concentrations associated with Arctic Haze. In this study, we evaluate sulfate and BC concentrations from eleven different models driven with the same emission inventory against a comprehensive pan-Arctic measurement data set over a time period of 2 years (2008–2009). The set of models consisted of one Lagrangian particle dispersion model, four chemistry transport models (CTMs), one atmospheric chemistry-weather forecast model and five chemistry climate models (CCMs), of which two were nudged to meteorological analyses and three were running freely. The measurement data set consisted of surface measurements of equivalent BC (eBC) from five stations (Alert, Barrow, Pallas, Tiksi and Zeppelin), elemental carbon (EC) from Station Nord and Alert and aircraft measurements of refractory BC (rBC) from six different campaigns. We find that the models generally captured the measured eBC or rBC and sulfate concentrations quite well, compared to previous comparisons. However, the aerosol seasonality at the surface is still too weak in most models. Concentrations of eBC and sulfate averaged over three surface sites are underestimated in winter/spring in all but one model (model means for January–March underestimated by 59 and 37 % for BC and sulfate, respectively), whereas concentrations in summer are overestimated in the model mean (by 88 and 44 % for July–September), but with overestimates as well as underestimates present in individual models. The most pronounced eBC underestimates, not included in the above multi-site average, are found for the station Tiksi in Siberia where the measured annual mean eBC concentration is 3 times higher than the average annual mean for all other stations. This suggests an underestimate of BC sources in Russia in the emission inventory used. Based on the campaign data, biomass burning was identified as another cause of the modeling problems. For sulfate, very large differences were found in the model ensemble, with an apparent anti-correlation between modeled surface concentrations and total atmospheric columns. There is a strong correlation between observed sulfate and eBC concentrations with consistent sulfate/eBC slopes found for all Arctic stations, indicating that the sources contributing to sulfate and BC are similar throughout the Arctic and that the aerosols are internally mixed and undergo similar removal. However, only three models reproduced this finding, whereas sulfate and BC are weakly correlated in the other models. Overall, no class of models (e.g., CTMs, CCMs) performed better than the others and differences are independent of model resolution
Searches for Ultra-High-Energy Photons at the Pierre Auger Observatory
The Pierre Auger Observatory, being the largest air-shower experiment in the
world, offers an unprecedented exposure to neutral particles at the highest
energies. Since the start of data taking more than 18 years ago, various
searches for ultra-high-energy (UHE, ) photons have
been performed: either for a diffuse flux of UHE photons, for point sources of
UHE photons or for UHE photons associated with transient events like
gravitational wave events. In the present paper, we summarize these searches
and review the current results obtained using the wealth of data collected by
the Pierre Auger Observatory.Comment: Review article accepted for publication in Universe (special issue on
ultra-high energy photons
The Pierre Auger Observatory Open Data
The Pierre Auger Collaboration has embraced the concept of open access to
their research data since its foundation, with the aim of giving access to the
widest possible community. A gradual process of release began as early as 2007
when 1% of the cosmic-ray data was made public, along with 100% of the
space-weather information. In February 2021, a portal was released containing
10% of cosmic-ray data collected from 2004 to 2018, during Phase I of the
Observatory. The Portal included detailed documentation about the detection and
reconstruction procedures, analysis codes that can be easily used and modified
and, additionally, visualization tools. Since then the Portal has been updated
and extended. In 2023, a catalog of the 100 highest-energy cosmic-ray events
examined in depth has been included. A specific section dedicated to
educational use has been developed with the expectation that these data will be
explored by a wide and diverse community including professional and
citizen-scientists, and used for educational and outreach initiatives. This
paper describes the context, the spirit and the technical implementation of the
release of data by the largest cosmic-ray detector ever built, and anticipates
its future developments.Comment: 19 pages, 8 figure
Radio Measurements of the Depth of Air-Shower Maximum at the Pierre Auger Observatory
The Auger Engineering Radio Array (AERA), part of the Pierre Auger
Observatory, is currently the largest array of radio antenna stations deployed
for the detection of cosmic rays, spanning an area of km with 153
radio stations. It detects the radio emission of extensive air showers produced
by cosmic rays in the MHz band. Here, we report the AERA measurements
of the depth of the shower maximum (), a probe for mass
composition, at cosmic-ray energies between to eV,
which show agreement with earlier measurements with the fluorescence technique
at the Pierre Auger Observatory. We show advancements in the method for radio
reconstruction by comparison to dedicated sets of CORSIKA/CoREAS
air-shower simulations, including steps of reconstruction-bias identification
and correction, which is of particular importance for irregular or sparse radio
arrays. Using the largest set of radio air-shower measurements to date, we show
the radio resolution as a function of energy, reaching a
resolution better than g cm at the highest energies, demonstrating
that radio measurements are competitive with the established
high-precision fluorescence technique. In addition, we developed a procedure
for performing an extensive data-driven study of systematic uncertainties,
including the effects of acceptance bias, reconstruction bias, and the
investigation of possible residual biases. These results have been
cross-checked with air showers measured independently with both the radio and
fluorescence techniques, a setup unique to the Pierre Auger Observatory.Comment: Submitted to Phys. Rev.
Constraining models for the origin of ultra-high-energy cosmic rays with a novel combined analysis of arrival directions, spectrum, and composition data measured at the Pierre Auger Observatory
The combined fit of the measured energy spectrum and shower maximum depth distributions of ultra-high-energy cosmic rays is known to constrain the parameters of astrophysical models with homogeneous source distributions. Studies of the distribution of the cosmic-ray arrival directions show a better agreement with models in which a fraction of the flux is non-isotropic and associated with the nearby radio galaxy Centaurus A or with catalogs such as that of starburst galaxies. Here, we present a novel combination of both analyses by a simultaneous fit of arrival directions, energy spectrum, and composition data measured at the Pierre Auger Observatory. The model takes into account a rigidity-dependent magnetic field blurring and an energy-dependent evolution of the catalog contribution shaped by interactions during propagation. We find that a model containing a flux contribution from the starburst galaxy catalog of around 20% at 40 EeV with a magnetic field blurring of around 20° for a rigidity of 10 EV provides a fair simultaneous description of all three observables. The starburst galaxy model is favored with a significance of 4.5σ (considering experimental systematic effects) compared to a reference model with only homogeneously distributed background sources. By investigating a scenario with Centaurus A as a single source in combination with the homogeneous background, we confirm that this region of the sky provides the dominant contribution to the observed anisotropy signal. Models containing a catalog of jetted active galactic nuclei whose flux scales with the γ-ray emission are, however, disfavored as they cannot adequately describe the measured arrival directions
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