Variable Selection for 1D Regression Models

Variable selection, the search for j relevant predictor variables from a group of p candidates, is a standard problem in regression analysis. The class of 1D regression models is a broad class that includes generalized linear models. We show that existing variable selection algorithms, originally meant for multiple linear regression and based on ordinary least squares and Mallows’ Cp, can also be used for 1D models. Graphical aids for variable selection are also provided

Behavior of Elemental Sets in Regression

Elemental sets are used to produce trial estimates b of the regression coefficients β. If b0 minimizes ||b-β|| among all elemental fits b, then ||b0-β||=OP(n-1), regardless of the criterion used. For any estimator bA, ||bA-β|| is at best OP(n-1/2). Hence restricting fits to elemental introduces asymptotically negligible error

Robust Regression with High Coverage

An important parameter for several high breakdown regression algorithm estimators is the number of cases given weight one, called the coverage of the estimator. Increasing the coverage is believed to result in a more stable estimator, but the price paid for this stability is greatly decreased resistance to outliers. A simple modification of the algorithm can greatly increase the coverage and hence its statistical performance while maintaining high outlier resistance

Inconsistency of Resampling Algorithms for High Breakdown Regression Estimators and a New Algorithm

Since high breakdown estimators are impractical to compute exactly in large samples, approximate algorithms are used. The algorithm generally produces an estimator with a lower consistency rate and breakdown value than the exact theoretical estimator. This discrepancy grows with the sample size, with the implication that huge computations are needed for good approximations in large high-dimensioned samples The workhorse for HBE has been the ‘elemental set’, or ‘basic resampling’ algorithm. This turns out to be completely ineffective in high dimensions with high levels of contamination. However, enriching it with a “concentration” step turns it into a method that is able to handle even high levels of contamination, provided the regression outliers are located on random cases. It remains ineffective if the regression outliers are concentrated on high leverage cases. We focus on the multiple regression problem, but several of the broad conclusions – notably those of the inadequacy of fixed numbers of elemental starts – are relevant to multivariate location and dispersion estimation as well. We introduce a new algorithm – the “X-cluster” method – for large high-dimensional multiple regression data sets that are beyond the reach of standard resampling methods. This algorithm departs sharply from current HBE algorithms in that, even at a constant percentage of contamination, it is more effective the larger the sample, making a compelling case for using it in the large-sample situations that current methods serve poorly. A multi-pronged analysis, using both traditional OLS and L1 methods along with newer resistant techniques, will often detect departures from the multiple regression model that can not be detected by any single estimator

Laroche and the Seals of Meskene-Emar

Introduction An international colloquium “Les écritures mises au jour sur le site antique d’Ougarit (Syrie) et leur déchiffrement, 1930-2010” was held in December 2010 in the Collège de France and the Académie des Inscriptions et Belles-Lettres, and the Actes de colloque have recently appeared (Bordreuil et al. 2014 (éds.)). When invited to give a paper, I felt it appropriate to speak on “The digraphic seals of Ugarit: Emmanuel Laroche and the decipherment of Hieroglyphic Luwian”. In this pap..

Randomised, controlled trial of alternating pressure mattresses compared with alternating pressure overlays for the prevention of pressure ulcers : PRESSURE (pressure relieving support surfaces) trial

Objective To compare whether differences exist between alternating pressure overlays and alternating pressure mattresses in the development of new pressure ulcers, healing of existing pressure ulcers, and patient acceptability. Design Pragmatic, open, multicentre, randomised controlled trial. Setting 11 hospitals in six NHS trusts. Participants 1972 people admitted to hospital as acute or elective patients. Interventions Participants were randomised to an alternating pressure mattress (n = 982) of- an alternating pressure overlay (n = 990). Main outcome measures The proportion of participants developing a new pressure ulcer of grade 2 or worse; time to development of new pressure ulcers; proportions of participants developing a new ulcer within 30 days; healing of existing pressure ulcers; and patient acceptability Results Intention to treat analysis found no difference in the proportions of participants developing a new pressure ulcer of grade 2 or worse (10.7% overlay patients, 10.3% mattress patients; difference 0.4%, 95% confidence interval - 23% to 3.1%, P = 0.75). More overlay patients requested change owing to dissatisfaction (23.3%) than mattress patients (18.9%, P = 0.02). Conclusion No difference was found between alternating pressure mattresses and alternating pressure overlays in the proportion of people who develop a pressure ulcer

Erupting Dwarf Novae in the Large Magellanic Cloud

We report the first likely detections of erupting Dwarf Novae (DN) in an external galaxy: the Large Magellanic Cloud. Six candidates were isolated from approximately a million stars observed every second night over 11 nights with the CTIO 8K x 8K Mosaic2 CCD imager. Artificial dwarf nova and completeness tests suggest that we are seeing only the brightest of the LMC DN, probably SS Cygni-like CVs, but possibly SU UMa-type cataclysmics undergoing superoutbursts. We derive crude but useful limits on the LMC DN surface density, and on the number of DN in the LMC. Many thousands of cataclysmic variables in the Magellanic Clouds can be discovered and characterized with 8 meter class telescopes.Comment: Accepted for publication in AJ, 28 pages, 9 figures total, Figures 1 and 8 are supplied separately in jpeg forma

Providing Economic Incentives in Environmental Regulation

CHAIRMAN BREGER: Let me welcome you to this AdministrativeConference colloquy on providing economic incentives in environmentallitigation

Kizzuwatna and the Euphrates States: Kummaha, Elbistan, Malatya Philology

Summary of philological evidence for Hittite Geography regarding KIzzuwatna and the Euphrates States