7,983 research outputs found
Common scale valuations across different preference-based measures: estimation using rank data
Background: Different preference-based measures (PBMs) used to estimate Quality Adjusted Life Years (QALYs) provide di¤erent utility values for the same patient. Differences are expected since values have been obtained using different samples, valuation techniques and descriptive systems. Previous studies have estimated the relationship between pairs of PBMs using patient self-reported data. However, there is a need for an approach capable of generating values directly on a common scale for a range of PBMs using the same sample of general population respondents and valuation technique but keeping the advantages of the different descriptive systems.
Methods: General public survey data (n=501) where respondents ranked health states described using subsets of six PBMs were analysed. We develop a new model based on the mixed logit to overcome two key limitations of the standard rank ordered logit model, namely, the unrealistic choice pattern (Independence of Irrelevant Alternatives) and the independence of repeated observations.
Results: There are substantial differences in the estimated parameters between the two models (mean di¤erence 0.07) leading to di¤erent orderings across the measures. Estimated values for the best states described by di¤erent PBMs are substantially and significantly di¤erent using the standard model, unlike our approach which yields more consistent results.
Limitations: Data come from a exploratory study that is relatively small both in sample size and coverage of health states.
Conclusions: This study develops a new, �exible econometric model specifically designed to reflect appropriately the features of rank data. Results support the view that the standard model is not appropriate in this setting and will yield very different and apparently inconsistent results. PBMs can be compared using a common scale by implementation of this new approach
String Field Theory from IIB Matrix Model
We derive Schwinger-Dyson equations for the Wilson loops of a type IIB matrix
model. Superstring coordinates are introduced through the construction of the
loop space. We show that the continuum limit of the loop equation reproduces
the light-cone superstring field theory of type IIB superstring in the large-N
limit. We find that the interacting string theory can be obtained in the double
scaling limit as it is expected.Comment: 21 pages, Latex, 1 figur
Estimation of a preference based single index from the sexual quality of life questionnaire (SQOL) using ordinal data
There is increasing interest in using ordinal methods to estimate cardinal values for health states to calculate quality adjusted life years. This paper reports the estimation of models of rank data and discrete choice experiment (DCE) data to derive a preference-based index from a condition specific measure relating to sexual health and to compare the results to values generated from time trade-off valuation (TTO). The DCE data were analysed using a random effects probit model and the DCE predicted values were rescaled according to the highest and lowest predicted TTO values corresponding to the best and worst SQOL health states respectively. The rank data were analysed using a rank ordered logit model and re-scaled using two alternative methods. Firstly, re-scaling the rank predicted values using identical methods to those employed for DCE and secondly, re-scaling the rank model coefficients by dividing each level coefficient by the coefficient relating to death. The study raises some important issues about the use of ordinal data to produce cardinal health state valuations
Transport mechanism through metal-cobaltite interfaces
The resistive switching (RS) properties as a function of temperature were
studied for Ag/LaSrCoO (LSCO) interfaces. The LSCO is a
fully-relaxed 100 nm film grown by metal organic deposition on a LaAlO
substrate. Both low and a high resistance states were set at room temperature
and the temperature dependence of their current-voltage (IV) characteristics
was mea- sured taking care to avoid a significant change of the resistance
state. The obtained non-trivial IV curves of each state were well reproduced by
a circuit model which includes a Poole-Frenkel element and two ohmic
resistances. A microscopic description of the changes produced by the RS is
given, which enables to envision a picture of the interface as an area where
conductive and insulating phases are mixed, producing Maxwell-Wagner
contributions to the dielectric properties.Comment: 13 pages, 5 figures, to be published in APL. Corresponding author: C.
Acha ([email protected]
Pulsed-Source MOCVD of High-k Dielectric Thin Films with in situ Monitoring by Spectroscopic Ellipsometry
Superfluidity of Dirac Fermions in a Tunable Honeycomb Lattice: Cooper Pairing, Collective Modes, and Critical Currents
Motivated by recent experiments on atomic Dirac fermions in a tunable
honeycomb optical lattice, we study the attractive Hubbard model of
superfluidity in the anisotropic honeycomb lattice. At weak-coupling, we find
that the maximum mean field pairing transition temperature, as a function of
density and interaction strength, occurs for the case with isotropic hopping
amplitudes. In this isotropic case, we go beyond mean field theory and study
collective fluctuations, treating both pairing and density fluctuations for
interaction strengths ranging from weak to strong coupling. We find evidence
for a sharp sound mode, together with a well-defined Leggett mode over a wide
region of the phase diagram. We also calculate the superfluid order parameter
and collective modes in the presence of nonzero superfluid flow. The
flow-induced softening of these collective modes leads to dynamical
instabilities involving stripe-like density modulations as well as a
Leggett-mode instability associated with the natural sublattice symmetry
breaking charge-ordered state on the honeycomb lattice. The latter provides a
non-trivial test for the experimental realization of the one-band Hubbard
model. We delineate regimes of the phase diagram where the critical current is
limited by depairing or by such collective instabilities, and discuss
experimental implications of our results.Comment: 20 pages, 12 figures. v3: published versio
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