19,421 research outputs found
Calibrated Weighting for Small Area Estimation
Calibrated weighting methods for estimation of survey population characteristics are widely used. At the same time, model-based prediction methods for estimation of small area or domain characteristics are becoming increasingly popular. This paper explores weighting methods based on the mixed models that underpin small area estimates to see whether they can deliver equivalent small area estimation performance when compared with standard prediction methods and superior population level estimation performance when compared with standard calibrated weighting methods. A simple MSE estimator for weighted small area estimation is also developed
Comment on Article by Ferreira and Gamerman
A utility-function approach to optimal spatial sampling design is a powerful
way to quantify what "optimality" means. The emphasis then should be to capture
all possible contributions to utility, including scientific impact and the cost
of sampling. The resulting sampling plan should contain a component of designed
randomness that would allow for a non-parametric design-based analysis if
model-based assumptions were in doubt. [arXiv:1509.03410]Comment: Published at http://dx.doi.org/10.1214/15-BA944B in the Bayesian
Analysis (http://projecteuclid.org/euclid.ba) by the International Society of
Bayesian Analysis (http://bayesian.org/
Minimal inference from incomplete 2x2-tables
Estimates based on 2x2 tables of frequencies are widely used in statistical
applications. However, in many cases these tables are incomplete in the sense
that the data required to compute the frequencies for a subset of the cells
defining the table are unavailable. Minimal inference addresses those
situations where this incompleteness leads to target parameters for these
tables that are interval, rather than point, identifiable. In particular, we
develop the concept of corroboration as a measure of the statistical evidence
in the observed data that is not based on likelihoods. The corroboration
function identifies the parameter values that are the hardest to refute, i.e.,
those values which, under repeated sampling, remain interval identified. This
enables us to develop a general approach to inference from incomplete 2x2
tables when the additional assumptions required to support a likelihood-based
approach cannot be sustained based on the data available. This minimal
inference approach then provides a foundation for further analysis that aims at
making sharper inference supported by plausible external beliefs
Microscopic picture of aging in SiO2
We investigate the aging dynamics of amorphous SiO2 via molecular dynamics
simulations of a quench from a high temperature T_i to a lower temperature T_f.
We obtain a microscopic picture of aging dynamics by analyzing single particle
trajectories, identifying jump events when a particle escapes the cage formed
by its neighbors, and by determining how these jumps depend on the waiting time
t_w, the time elapsed since the temperature quench to T_f. We find that the
only t_w-dependent microscopic quantity is the number of jumping particles per
unit time, which decreases with age. Similar to previous studies for fragile
glass formers, we show here for the strong glass former SiO2 that neither the
distribution of jump lengths nor the distribution of times spent in the cage
are t_w-dependent. We conclude that the microscopic aging dynamics is
surprisingly similar for fragile and strong glass formers.Comment: 4 pages, 7 figure
Computation of turbulent boundary layers on curved surfaces, 1 June 1975 - 31 January 1976
An accurate method was developed for predicting effects of streamline curvature and coordinate system rotation on turbulent boundary layers. A new two-equation model of turbulence was developed which serves as the basis of the study. In developing the new model, physical reasoning is combined with singular perturbation methods to develop a rational, physically-based set of equations which are, on the one hand, as accurate as mixing-length theory for equilibrium boundary layers and, on the other hand, suitable for computing effects of curvature and rotation. The equations are solved numerically for several boundary layer flows over plane and curved surfaces. For incompressible boundary layers, results of the computations are generally within 10% of corresponding experimental data. Somewhat larger discrepancies are noted for compressible applications
Time to address the double inequality of differences in dietary intake between Scotland and England
Geographical disparities in health outcomes have been evident across the UK for decades. There is limited recent analysis on the dietary differences between Scotland and England that might go some way to explain these health differences. This study aimed to assess whether, and to what degree, aspects of diet and nutrition differ between Scottish and English populations, specifically between those with similar household incomes. Twelve years of UK food purchase data (2001-2012) were pooled and used to estimate household level consumption data for Scotland and England. Population mean food consumption and nutrient intakes were estimated, adjusting for known confounders (year, age of household reference person, age they left full-time education and income). Comparison was also made within equivalised income quintiles. Analysis showed that the foods and nutrients that should be increased in the diet (highlighted in the Scottish Dietary Goals) were lower in Scotland than England (e.g. fruit and vegetables 267g/day (99%CI 259-274g/day) vs. 298g/day (99%CI 296-301g/day), P<0.001). Likewise, foods and drinks linked with poor health outcomes were higher in Scotland. These regional inequalities in diet were even more pronounced in the lower income groups (e.g. red and processed meat consumption in the lowest income quintile was 65g/day (99% CI 61-69g/day) in Scotland vs. 58g/day (99% CI 57-60g/day) in England, P<0.001, but similar in the highest income quintile (58g/day (99%CI 54-61 g/day) vs. 59g/day (99% CI 58-60 g/day) respectively). A poorer diet in Scotland compared to England, particularly among disadvantaged groups, may contribute to differences in excess mortality between countries
Results of recent NASA studies on automatic spin prevention for fighter aircraft
A broad based research program was developed to eliminate or minimize inadvertent spins for advanced military aircraft. Recent piloted simulator studies and airplane flight tests have demonstrated that the automatic control systems in use on current fighters can be tailored to provide a high degree of spin resistance for some configurations without restrictions to maneuverability. Such systems result in greatly increased tactical effectiveness, safety, and pilot confidence
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Periportal Capsulotomy: A Technique for Limited Violation of the Hip Capsule During Arthroscopy for Femoroacetabular Impingement.
Hip arthroscopy has become the standard treatment for symptomatic femoroacetabular impingement as patients have shown good outcomes and high satisfaction with this intervention. However, capsular management to gain access for intra-articular procedures remains greatly debated. Capsular closure is advocated particularly in the setting of interportal or T-capsulotomy to avoid complications of instability or nonhealing capsule. We introduce a technique for capsular management through a limited periportal capsulotomy during arthroscopic treatment of femoroacetabular impingement. In using dilation of the anterolateral and mid-anterior portals without completion of a full interportal capsulotomy, the stabilizing iliofemoral ligament is preserved. We have found that periportal capsulotomy provides safe and sufficient access to the hip joint without necessitating capsular closure
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