Identifying Treatment Effects using Trimmed Means when Data are Missing Not at Random

Patients often discontinue treatment in a clinical trial because their health condition is not improving. Consequently, the patients still in the study at the end of the trial have better health outcomes on average than the initial patient population would have had if every patient had completed the trial. If we only analyze the patients who complete the trial, then this missing data problem biases the estimator of a medication's efficacy because study outcomes are missing not at random (MNAR). One way to overcome this problem - the trimmed means approach for missing data - sets missing values as slightly worse than the worst observed outcome and then trims away a fraction of the distribution from each treatment arm before calculating differences in treatment efficacy (Permutt 2017, Pharmaceutical statistics 16.1:20-28). In this paper we derive sufficient and necessary conditions for when this approach can identify the average population treatment effect in the presence of MNAR data. Numerical studies show the trimmed means approach's ability to effectively estimate treatment efficacy when data are MNAR and missingness is strongly associated with an unfavorable outcome, but trimmed means fail when data are missing at random (MAR) when the better approach would be to multiply impute the missing values. If the reasons for discontinuation in a clinical trial are known analysts can improve estimates with a combination of multiple imputation (MI) and the trimmed means approach when the assumptions of each missing data mechanism hold. When the assumptions are justifiable, using trimmed means can help identify treatment effects notwithstanding MNAR data

Создание износостойких покрытий, наплавленных в пучке релятивистских электронов

Целью работы является исследование структуры и свойств (твердости, износостойкости, коррозионной стойкости) покрытий, наплавленных в пучке релятивистских электронов, от характера их легирования с наплавочной порошковой смеси при применении в качестве главных легирующих добавок хрома, углерода и бора, нахождение оптимальных составов наплавочных смесей и получение неоднородных структур с включениями твердой фазы, обладающих в то же время высокой износостойкостью и коррозионной стойкостью и способных заменить при наплавке дорогой карбид вольфрама.The aim of this work is to study the structure and properties (hardness, wear resistance, corrosion resistance) of coatings deposited in a beam of relativistic electrons, on the nature of their alloying from the surfacing powder mixture when used as the main alloying additives of chromium, carbon and boron, finding the optimum compositions of the surfacing mixtures and obtaining heterogeneous structures with inclusions of the solid phase, which at the same time have high wear resistance and corrosion resistance and are able to replace when surfacing an expensive car tungsten bide

Deposition and solubility of airborne metals to four plant species grown at varying distances from two heavily trafficked roads in London

In urban areas, a highly variable mixture of pollutants is deposited as particulate matter. The concentration and bioavailability of individual pollutants within particles need to be characterised to ascertain the risks to ecological receptors. This study, carried out at two urban parks, measured the deposition and water-solubility of metals to four species common to UK urban areas. Foliar Cd, Cr, Cu, Fe, Ni, Pb and Zn concentrations were elevated in at least one species compared with those from a rural control site. Concentrations were, however, only affected by distance to road in nettle and, to a lesser extent, birch leaves. Greater concentrations of metal were observed in these species compared to cypress and maple possibly due to differences in plant morphology and leaf surfaces. Solubility appeared to be linked to the size fraction and, therefore, origin of the metal with those present predominantly in the coarse fraction exhibiting low solubility. © 2009

Carl Wilhelm Nose (1753-1835) zum 150. Todestag

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Die "Vormalige Verknüpfung und Absonderung der alten und neuen Welt"; eine Abhandlung des Freiherrn von Hüpsch aus dem Jahre 1764

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