5,923 research outputs found
Evaluating and extending a Bayesian approach to using historical control data in an actively controlled non-inferiority clinical trial
Obstacles sometimes limit enrollment in randomized clinical trials of an exper- imental product versus an active control, making it desirable to augment the ran- domized control group with historical control groups. However, bias between control groups with respect to the mean outcome could lead to spurious conclusions. Meth- ods are necessary that allow for the combination of control groups while controlling for bias.
Pocock (1976) developed a Bayesian test to address this need, but it requires sub- jective specification of the variance of the bias between the randomized and historical control groups and is designed to include only a single historical control group. In the context of an actively controlled non-inferiority trial, we extend his method on three fronts. First, we replace subjective specification of the variance of the bias with empirically driven estimates. Second, we develop an adaptive design that re-powers a trial based on an interim estimate of the variance of the bias using observed data. Third, we modify the test to include multiple historical control groups.
When including a single historical control group, simulations show that the true bias, if known, can be used in place of the variance of the bias, and that this estimate ivmaintains Type I Error with no loss in power as compared to using the true variance of the bias. Further, we show that using an empirical estimate of the bias to estimate the variance of bias may result in moderately inflated Type I Error, but that using a conservative estimate of the bias (the upper bound of a 90% confidence interval) maintains Type I Error. Simulations also demonstrate that using an estimate of the bias at the interim and conclusion provides designed power but may result in moder- ately inflated Type I Error. Therefore, a conservative estimate of the bias should be used at trial end when using this approach. Lastly, it is shown that if an adequate number of multiple historical control groups are available, the modified test maintains Type I Error when using bias estimates. These methods provide objective guidance on parameter estimation, but further research is necessary in order to improve power
Federal Liens
It is the purpose of this paper to discuss the various liens, arising under United States laws or statutes, that may affect the title to real estate. Since the writer discussed the subject of bankruptcy at the 1922 meeting of this association no discusison of that subject is included in this paper
SIMES ON FUTURE INTERESTS
It is encouraging that the law teachers are turning their talents to the writing of treatises. Recent examples are Professor Bogert\u27s monumental work on Trusts and Professor Griswold\u27s volume on Spendthrift Trusts. And now comes this comprehensive work on Future Interests, about which little has heretofore been written with an especial appeal to the average practitioner. Too much of the law teacher\u27s energy has. gone into editing case books and writing law review articles. And case books and law review articles are not read by lawyers in general
AN AGRICULTURAL VALUE TAX AS AN ALTERNATIVE TO LAND USE TAX OR MARKET VALUE TAX ON LAND
Public Economics,
Demonstration of non-Markovian process characterisation and control on a quantum processor
In the scale-up of quantum computers, the framework underpinning
fault-tolerance generally relies on the strong assumption that environmental
noise affecting qubit logic is uncorrelated (Markovian). However, as physical
devices progress well into the complex multi-qubit regime, attention is turning
to understanding the appearance and mitigation of correlated -- or
non-Markovian -- noise, which poses a serious challenge to the progression of
quantum technology. This error type has previously remained elusive to
characterisation techniques. Here, we develop a framework for characterising
non-Markovian dynamics in quantum systems and experimentally test it on
multi-qubit superconducting quantum devices. Where noisy processes cannot be
accounted for using standard Markovian techniques, our reconstruction predicts
the behaviour of the devices with an infidelity of . Our results show
this characterisation technique leads to superior quantum control and extension
of coherence time by effective decoupling from the non-Markovian environment.
This framework, validated by our results, is applicable to any controlled
quantum device and offers a significant step towards optimal device operation
and noise reduction
What have we already learned from the CMB?
The COBE satellite, and the DMR experiment in particular, was extraordinarily
successful. However, the DMR results were announced about 7 years ago, during
which time a great deal more has been learned about anisotropies in the Cosmic
Microwave Background (CMB). The CMB experiments currently being designed and
built, including long-duration balloons, interferometers, and two space
missions, promise to address several fundamental cosmological issues. We
present our evaluation of what we already know, what we are beginning to learn
now, and what the future may bring.Comment: 20 pages, 3 figures. Changes to match version accepted by PAS
The Born and Lens-Lens Corrections to Weak Gravitational Lensing Angular Power Spectra
We revisit the estimation of higher order corrections to the angular power
spectra of weak gravitational lensing. Extending a previous calculation of
Cooray and Hu, we find two additional terms to the fourth order in potential
perturbations of large-scale structure corresponding to corrections associated
with the Born approximation and the neglect of line-of-sight coupling of two
foreground lenses in the standard first order result. These terms alter the
convergence (), the lensing shear E-mode (),
and their cross-correlation () power spectra on large angular
scales, but leave the power spectra of the lensing shear B-mode ()
and rotational () component unchanged as compared to previous
estimates. The new terms complete the calculation of corrections to weak
lensing angular power spectra associated with both the Born approximation and
the lens-lens coupling to an order in which the contributions are most
significant. Taking these features together, we find that these corrections are
unimportant for any weak lensing survey, including for a full sky survey
limited by cosmic variance.Comment: Added references, minor changes to text. 9 pages, 2 figure
Geodatabase Development to Support Hyperspectral Imagery Exploitation
Geodatabase development for coastal studies conducted by the Naval Research Laboratory (NRL) is essential to support the exploitation of hyperspectral imagery (HSI). NRL has found that the remote sensing and mapping science community benefits from coastal classifications that group coastal types based on similar features. Selected features in project geodatabases relate to significant biological and physical forces that shape the coast. The project geodatabases help researchers understand factors that are necessary for imagery post processing, especially those features having a high degree of temporal and spatial variability. NRL project geodatabases include a hierarchy of environmental factors that extend from shallow water bottom types and beach composition to inland soil and vegetation characteristics. These geodatabases developed by NRL allow researchers to compare features among coast types. The project geodatabases may also be used to enhance littoral data archives that are sparse. This paper highlights geodatabase development for recent remote sensing experiments in barrier island, coral, and mangrove coast types
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