Search results for "Wald"
showing 10 items of 81 documents
Adaptive designs with correlated test statistics
2009
In clinical trials, the collected observations such as clustered data or repeated measurements are often correlated. As a consequence, test statistics in a multistage design are correlated. Adaptive designs were originally developed for independent test statistics. We present a general framework for two-stage adaptive designs with correlated test statistics. We show that the significance level for the Bauer-Köhne design is inflated for positively correlated test statistics from a bivariate normal distribution. The decision boundary for the second stage can be modified so that type one error is controlled. This general concept is expandable to other adaptive designs. In order to use these de…
The “ThreePlusOne” Likelihood-Based Test Statistics: Unified Geometrical and Graphical Interpretations
2014
The presentation of the well known Likelihood Ratio, Wald and Score test statistics in textbooks appears to lack a unified graphical and geometrical interpretation. We present two simple graphical representations on a common scale for these three test statistics, and also the recently proposed Gradient test statistic. These unified graphical displays may favour better understanding of the geometrical meaning of the likelihood based statistics and provide useful insights into their connections.
Inferential tools in penalized logistic regression for small and sparse data: A comparative study.
2016
This paper focuses on inferential tools in the logistic regression model fitted by the Firth penalized likelihood. In this context, the Likelihood Ratio statistic is often reported to be the preferred choice as compared to the ‘traditional’ Wald statistic. In this work, we consider and discuss a wider range of test statistics, including the robust Wald, the Score, and the recently proposed Gradient statistic. We compare all these asymptotically equivalent statistics in terms of interval estimation and hypothesis testing via simulation experiments and analyses of two real datasets. We find out that the Likelihood Ratio statistic does not appear the best inferential device in the Firth penal…
The Induced Smoothed lasso: A practical framework for hypothesis testing in high dimensional regression.
2020
This paper focuses on hypothesis testing in lasso regression, when one is interested in judging statistical significance for the regression coefficients in the regression equation involving a lot of covariates. To get reliable p-values, we propose a new lasso-type estimator relying on the idea of induced smoothing which allows to obtain appropriate covariance matrix and Wald statistic relatively easily. Some simulation experiments reveal that our approach exhibits good performance when contrasted with the recent inferential tools in the lasso framework. Two real data analyses are presented to illustrate the proposed framework in practice.
Zur Stereochemie der Oxidation chiraler, tertiärer Phosphine mit Dimethylsulfoxid
1976
Es wird uber den sterischen Verlauf der Oxidation der optisch aktiven, tertiaren Phosphine 3 and 4 mit Dimethylsulfoxid berichtet. Diese Umsetzung verlauft nur in Gegenwart elektrophiler Katalysatoren (Tabelle 1). Je nach Art and Menge des Katalysators zeigt die Stereochemie der Reaktion entweder uberwiegende Inversion oder Retention der Konfiguration am Phosphor an (Tabellen 2, 3); in einigen Fallen wird jedoch fast vollstandige Racemisierung beobachtet (Tabelle3). Auf der Grundlage dieser stereochemischen Resultate werden mogliche Mechanismen fur diese Umsetzung diskutiert. The Sterochemistry of the Oxidation of Chiral Tertiary Phosphines by Means of Dimethyl Sulfoxide The steric course o…
Phylogenetic analysis of the Antarctic genus Oswaldella Stechow, 1919 (Hydrozoa, Leptomedusae, Kirchenpaueriidae)
1999
A cladistic study was carried out on known species of the characteristically Antarctic genus Oswaldella, adopting as out-groups some other genera included in the family Kirchenpaueriidae. The analysis resulted in a cladogram with low CI in which no relationship between genera can be depicted. However, the hypothesis of monophyly of the genus Oswaldella is corroborated, being supported in our cladogram by five synapomorphies (although all are homoplastic with other taxa or reversed within the species of the genus). The basal relationships of the genus are uncertain, but three species groups are distinguishable within Oswaldella: 1) the O. incognita group, 2) the O. Antarctica group, and 3) a…
Chronology for the Cueva Victoria fossil site (SE Spain): Evidence for Early Pleistocene Afro-Iberian dispersals
2014
Cueva Victoria has provided remains of more than 90 species of fossil vertebrates, including a hominin phalanx, and the only specimens of the African cercopithecid Theropithecus oswaldi in Europe. To constrain the age of the vertebrate remains we used paleomagnetism, vertebrate biostratigraphy and (230)Th/U dating. Normal polarity was identified in the non-fossiliferous lowest and highest stratigraphic units (red clay and capping flowstones) while reverse polarity was found in the intermediate stratigraphic unit (fossiliferous breccia). A lower polarity change occurred during the deposition of the decalcification clay, when the cave was closed and karstification was active. A second polarit…
Hypothesis testing for Panels of Semi-Markov Processes with parametric sojourn time distributions
2022
This work deals with the asymptotic properties of maximum likelihood estimators for semi-Markov processes with parametric sojourn time distributions. It is motivated by the comparison, via a two-sample test procedure, of the distribution of two panels of qualitative trajectories modeled by semi-Markov processes and observed over a random number of transitions. Considering first one panel of growing size, we derive, under classical conditions, the convergence in probability of the estimators of the transition probabilities and the parameters of the sojourn time distributions as well as their asymptotic normality. We then consider panels of semi-Markov processes drawn from two different popul…
Estudio, mendiante electroscopía electrónica de barrido, de 16 especies del género Oswaldella Stechow, 1919 (Cnidaria: Hidrozoa)
2013
El género Oswaldella Stechow (1919) es el género de hidrozoos antárticos más diverso y uno de los géneros de invertebrados más abundante de los fondos oceánicos del sur de nuestro planeta. En este estudio se emplea la microscopía electrónica de barrido (MEB) para detallar numerosas características morfológicas de este género hasta ahora poco conocidas. En concreto, el número de nematotecas axilares, la forma de las nematotecas caulinares y de las hidrotecas adquieren un nuevo significado a través de este instrumento. En concreto, observamos que estas caracteríticas morfológicas parece variar mucho más de lo que en anteriores estudios con microscopía óptica se había observado. Se hace, ademá…
Combined Immuno-Chemotherapy (R-CHOP) Results in Significantly Superior Response Rates and Time to Treatment Failure in First Line Treatment of Patie…
2004
Abstract Lymphomplasmocytoid/ic immunocytoma (LP-IC), including Waldenstrom’s macro-globulinemia and lymphoplasmacytoid lymphoma according to the Kiel classification (the latter one subsummed as a variant of B-CLL in the WHO classification), is an indolent lymphoma, which is incurable by conventional chemotherapy in the advanced stage of disease. The anti-CD20 antibody Rituximab has shown remarkable activity in indolent lymphomas, in particular when combined with chemotherapy. Based on these results the GLSG investigated the efficacy of a combined immuno-chemotherapy (R-CHOP: Rituximab 375 mg/m2 d0-1; cyclophosphamide 750 mg/m2 d1; doxorubicine 50 mg/m2 d1; vincristine 1.4 mg/m2 d1; prednis…