7,487 research outputs found
Mind the gap! A multilevel analysis of factors related to variation in published cost-effectiveness estimates within and between countries
Background. Published cost-effectiveness estimates can vary considerably, both within and between countries. Despite extensive discussion, little is known empirically about factors relating to these variations. Objectives. To use multilevel statistical modeling to integrate cost-effectiveness estimates from published economic evaluations to investigate potential causes of variation. Methods. Cost-effectiveness studies of statins for cardiovascular disease prevention were identified by systematic review. Estimates of incremental costs and effects were extracted from reported base case, sensitivity, and subgroup analyses, with estimates grouped in studies and in countries. Three bivariate models were developed: a cross-classified model to accommodate data from multinational studies, a hierarchical model with multinational data allocated to a single category at country level, and a hierarchical model excluding multinational data. Covariates at different levels were drawn from a long list of factors suggested in the literature. Results. We found 67 studies reporting 2094 cost-effectiveness estimates relating to 23 countries (6 studies reporting for more than 1 country). Data and study-level covariates included patient characteristics, intervention and comparator cost, and some study methods (e.g., discount rates and time horizon). After adjusting for these factors, the proportion of variation attributable to countries was negligible in the cross-classified model but moderate in the hierarchical models (14%â19% of total variance). Country-level variables that improved the fit of the hierarchical models included measures of income and health care finance, health care resources, and population risks. Conclusions. Our analysis suggested that variability in published cost-effectiveness estimates is related more to differences in study methods than to differences in national context. Multinational studies were associated with much lower country-level variation than single-country studies. These findings are for a single clinical question and may be atypical
Constraining Isocurvature Initial Conditions with WMAP 3-year data
We present constraints on the presence of isocurvature modes from the
temperature and polarization CMB spectrum data from the WMAP satellite alone,
and in combination with other datasets including SDSS galaxy survey and SNLS
supernovae. We find that the inclusion of polarization data allows the WMAP
data alone, as well as in combination with complementary observations, to place
improved limits on the contribution of CDM and neutrino density isocurvature
components individually. With general correlations, the upper limits on these
sub-dominant isocurvature components are reduced to ~60% of the first year WMAP
results, with specific limits depending on the type of fluctuations. If
multiple isocurvature components are allowed, however, we find that the data
still allow a majority of the initial power to come from isocurvature modes. As
well as providing general constraints we also consider their interpretation in
light of specific theoretical models like the curvaton and double inflation.Comment: 8 pages, 7 figures. Revised Sec 4 and Figs 3-4 post-publication to
correct an error for models with varying isocurvature spectral inde
Troposphere-stratosphere (surface-55 km) monthly general circulation statistics for the Northern Hemisphere-four year averages
This report presents four year averages of monthly mean Northern Hemisphere general circulation statistics for the period from 1 December 1978 through 30 November 1982. Computations start with daily maps of temperature for 18 pressure levels between 1000 and 0.4 mb that were supplied by NOAA/NMC. Geopotential height and geostrophic wind are constructed using the hydrostatic and geostrophic formulae. Fields presented in this report are zonally averaged temperature, mean zonal wind, and amplitude and phase of the planetary waves in geopotential height with zonal wavenumbers 1-3. The northward fluxes of heat and eastward momentum by the standing and transient eddies along with their wavenumber decomposition and Eliassen-Palm flux propagation vectors and divergences by the standing and transient eddies along with their wavenumber decomposition are also given. Large annual and interannual variations are found in each quantity especially in the stratosphere in accordance with the changes in the planetary wave activity. The results are shown both in graphic and tabular form
THERMAL RADIATION FROM MAGNETIZED NEUTRON STARS: A look at the Surface of a Neutron Star.
Surface thermal emission has been detected by ROSAT from four nearby young
neutron stars. Assuming black body emission, the significant pulsations of the
observed light curves can be interpreted as due to large surface temperature
differences produced by the effect of the crustal magnetic field on the flow of
heat from the hot interior toward the cooler surface. However, the energy
dependence of the modulation observed in Geminga is incompatible with blackbody
emission: this effect will give us a strong constraint on models of the neutron
star surface.Comment: 10 pages. tar-compressed and uuencoded postcript file. talk given at
the `Jubilee Gamow Seminar', St. Petersburg, Sept. 1994
Gyrations: The Missing Link Between Classical Mechanics with its Underlying Euclidean Geometry and Relativistic Mechanics with its Underlying Hyperbolic Geometry
Being neither commutative nor associative, Einstein velocity addition of
relativistically admissible velocities gives rise to gyrations. Gyrations, in
turn, measure the extent to which Einstein addition deviates from commutativity
and from associativity. Gyrations are geometric automorphisms abstracted from
the relativistic mechanical effect known as Thomas precession
The Probability Density of the Higgs Boson Mass
The LEP Collaborations have reported a small excess of events in their
combined Higgs boson analysis at center of mass energies up to about 208 GeV.
In this communication, I present the result of a calculation of the probability
distribution function of the Higgs boson mass which can be rigorously obtained
if the validity of the Standard Model is assumed. It arises from the
combination of the most recent set of precision electroweak data and the
current results of the Higgs searches at LEP 2.Comment: 3 pages, 2 figure
Triple correlation for detection of damage-related nonlinearities in composite structures
Nonlinear effects in vibration responses are investigated for the undamaged composite plate and the composite plate with a delamination. The analysis is focused on higher harmonic generation in vibration responses for various excitation amplitude levels. This effect is investigated using the triple correlation technique. The dynamics of composite plate was modelled using two-dimensional finite elements and the classical lamination theory. The doubled-node approach was used to model delamination area. Mode shapes and natural frequencies were estimated based on numerical models. Next, the delamination divergence analysis was used to obtain relative displacements for delaminated plies. Experimental modal analysis test was carried out to verify the numerical models. The two strongest vibration modes as well as two vibration modes with the smallest and largest motion level of delaminated plies were selected for nonlinear vibration test. The Fisher criterion was employed to verify the effectiveness and confidence level of the proposed technique. The results show that the method can be used not only to reveal nonlinearities, but also to reliably detect impact damage in composites. These results are confirmed using the statistical analysis
Incremental Material Flow Analysis with Bayesian Inference
Material Flow Analysis (MFA) is widely used to study the life-cycles of materials from production, through use, to reuse, recycling or disposal, in order to identify environmental impacts and opportunities to address them. However, development of this type of analysis is often constrained by limited data, which may be uncertain, contradictory, missing or over-aggregated.
This article proposes a Bayesian approach, in which uncertain knowledge about material flows is described by probability distributions. If little data is initially available, the model predictions will be rather vague. As new data is acquired, it is systematically incorporated to reduce the level of uncertainty.
After reviewing previous approaches to uncertainty in MFA, the Bayesian approach is introduced, and a general recipe for its application to Material Flow Analysis is developed. This is applied to map global production of steel, using Markov Chain Monte Carlo simulations. As well as aiding the analyst, who can get started in the face of incomplete data, this incremental approach to MFA also supports efforts to improve communication of results by transparently accounting for uncertainty throughout.ngineering and Physical Sciences Research Council. Grant Numbers: EP/K039326/1, EP/N02351x/
Harold Jeffreys's Theory of Probability Revisited
Published exactly seventy years ago, Jeffreys's Theory of Probability (1939)
has had a unique impact on the Bayesian community and is now considered to be
one of the main classics in Bayesian Statistics as well as the initiator of the
objective Bayes school. In particular, its advances on the derivation of
noninformative priors as well as on the scaling of Bayes factors have had a
lasting impact on the field. However, the book reflects the characteristics of
the time, especially in terms of mathematical rigor. In this paper we point out
the fundamental aspects of this reference work, especially the thorough
coverage of testing problems and the construction of both estimation and
testing noninformative priors based on functional divergences. Our major aim
here is to help modern readers in navigating in this difficult text and in
concentrating on passages that are still relevant today.Comment: This paper commented in: [arXiv:1001.2967], [arXiv:1001.2968],
[arXiv:1001.2970], [arXiv:1001.2975], [arXiv:1001.2985], [arXiv:1001.3073].
Rejoinder in [arXiv:0909.1008]. Published in at
http://dx.doi.org/10.1214/09-STS284 the Statistical Science
(http://www.imstat.org/sts/) by the Institute of Mathematical Statistics
(http://www.imstat.org
Modeling GRB 050904: Autopsy of a Massive Stellar Explosion at z=6.29
GRB 050904 at redshift z=6.29, discovered and observed by Swift and with
spectroscopic redshift from the Subaru telescope, is the first gamma-ray burst
to be identified from beyond the epoch of reionization. Since the progenitors
of long gamma-ray bursts have been identified as massive stars, this event
offers a unique opportunity to investigate star formation environments at this
epoch. Apart from its record redshift, the burst is remarkable in two respects:
first, it exhibits fast-evolving X-ray and optical flares that peak
simultaneously at t~470 s in the observer frame, and may thus originate in the
same emission region; and second, its afterglow exhibits an accelerated decay
in the near-infrared (NIR) from t~10^4 s to t~3 10^4 s after the burst,
coincident with repeated and energetic X-ray flaring activity. We make a
complete analysis of available X-ray, NIR, and radio observations, utilizing
afterglow models that incorporate a range of physical effects not previously
considered for this or any other GRB afterglow, and quantifying our model
uncertainties in detail via Markov Chain Monte Carlo analysis. In the process,
we explore the possibility that the early optical and X-ray flare is due to
synchrotron and inverse Compton emission from the reverse shock regions of the
outflow. We suggest that the period of accelerated decay in the NIR may be due
to suppression of synchrotron radiation by inverse Compton interaction of X-ray
flare photons with electrons in the forward shock; a subsequent interval of
slow decay would then be due to a progressive decline in this suppression. The
range of acceptable models demonstrates that the kinetic energy and circumburst
density of GRB 050904 are well above the typical values found for low-redshift
GRBs.Comment: 45 pages, 7 figures, and ApJ accepted. Revised version, minor
modifications and 1 extra figur
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