6,953 research outputs found
Cost-effectiveness analysis in R using a multi-state modelling survival analysis framework: a tutorial
This tutorial provides a step-by-step guide to performing cost-effectiveness analysis using a multi-state modelling approach. Alongside the tutorial we provide easy-to-use functions in the statistics package R. We argue this multi-state modelling approach using a package such as R has advantages over approaches where models are built in a spreadsheet package. In particular, using a syntax-based approach means there is a written record of what was done and the calculations are transparent. Reproducing the analysis is straightforward as the syntax just needs to be run again. The approach can be thought of as an alternative way to build a Markov decision analytic model, which also has the option to use a state-arrival extended approach if the Markov property does not hold. In the state-arrival extended multi-state model a covariate that represents patients’ history is included allowing the Markov property to be tested. We illustrate the building of multi-state survival models, making predictions from the models and assessing fits. We then proceed to perform a cost-effectiveness analysis including deterministic and probabilistic sensitivity analyses. Finally, we show how to create two common methods of visualising the results, namely cost-effectiveness planes and cost-effectiveness acceptability curves. The analysis is implemented entirely within R. It is based on adaptions to functions in the existing R package mstate, to accommodate parametric multi-state modelling which facilitates extrapolation of survival curves
CONSUMERS' WILLINGNESS TO PURCHASE LOCALLY PRODUCED AGRICULTURAL PRODUCTS: AN ANALYSIS OF AN INDIANA SURVEY
Using a survey of over 320 consumers from across the state of Indiana, we estimate an ordered probit model to determine the demographic and attitudinal factors which are most important in predicting the likelihood of consumers to purchase products that are produced within the state. Our results indicate that the willingness to purchase locally produced agricultural products increases with time of residency in the state, and we find a greater tendency for female consumers to purchase such products. We also find that quality perceptions play a critical role in these food purchase-decisions. We underscore the importance of maintaining minimum quality standards to maximize the effectiveness of state level agricultural promotion programs.Consumer/Household Economics,
The Mirage of Triangular Arbitrage in the Spot Foreign Exchange Market
We investigate triangular arbitrage within the spot foreign exchange market
using high-frequency executable prices. We show that triangular arbitrage
opportunities do exist, but that most have short durations and small
magnitudes. We find intra-day variations in the number and length of arbitrage
opportunities, with larger numbers of opportunities with shorter mean durations
occurring during more liquid hours. We demonstrate further that the number of
arbitrage opportunities has decreased in recent years, implying a corresponding
increase in pricing efficiency. Using trading simulations, we show that a
trader would need to beat other market participants to an unfeasibly large
proportion of arbitrage prices to profit from triangular arbitrage over a
prolonged period of time. Our results suggest that the foreign exchange market
is internally self-consistent and provide a limited verification of market
efficiency
Evidence of spontaneous spin polarized transport in magnetic nanowires
The exploitation of the spin in charge-based systems is opening revolutionary
opportunities for device architecture. Surprisingly, room temperature
electrical transport through magnetic nanowires is still an unresolved issue.
Here, we show that ferromagnetic (Co) suspended atom chains spontaneously
display an electron transport of half a conductance quantum, as expected for a
fully polarized conduction channel. Similar behavior has been observed for Pd
(a quasi-magnetic 4d metal) and Pt (a non-magnetic 5d metal). These results
suggest that the nanowire low dimensionality reinforces or induces magnetic
behavior, lifting off spin degeneracy even at room temperature and zero
external magnetic field.Comment: 4 pages, 3 eps fig
A discrete time-dependent method for metastable atoms in intense fields
The full-dimensional time-dependent Schrodinger equation for the electronic
dynamics of single-electron systems in intense external fields is solved
directly using a discrete method.
Our approach combines the finite-difference and Lagrange mesh methods. The
method is applied to calculate the quasienergies and ionization probabilities
of atomic and molecular systems in intense static and dynamic electric fields.
The gauge invariance and accuracy of the method is established. Applications to
multiphoton ionization of positronium and hydrogen atoms and molecules are
presented. At very high intensity above saturation threshold, we extend the
method using a scaling technique to estimate the quasienergies of metastable
states of the hydrogen molecular ion. The results are in good agreement with
recent experiments.Comment: 10 pages, 9 figure, 4 table
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