bluuebunny/crossref_metadata_2025_split huggingface dataset:
A new estimation procedure for a partially nonlinear model via a mixed‐effects approach
Authors: Li Runze , Nie Lei 
Published: February 2009

AbstractThe authors consider the estimation of the parametric component of a partially nonlinear semiparametric regression model whose nonparametric component is viewed as a nuisance parameter. They show how estimation can proceed through a nonlinear mixed‐effects model approach. They prove that under certain regularity conditions, the proposed estimate is consistent and asymptotically Gaussian. They investigate its finite‐sample properties through simulations and illustrate its use with data on the relation between the photosynthetically active radiation and the net ecosystem‐atmosphere exchange of carbon dioxide.
Testing noninferiority in three‐armed clinical trials based on likelihood ratio statistics
Authors: Munk Axel , Mielke Matthias , Freitag Gudrun , Skipka Guido 
Published: February 2009

AbstractClinical noninferiority trials with at least three groups have received much attention recently, perhaps due to the fact that regulatory agencies often require that a placebo group be evaluated along with a new experimental drug and an active control. The authors discuss likelihood ratio tests for binary endpoints and various noninferiority hypotheses. They find that, depending on the particular hypothesis, the test reduces asymptotically either to the intersection‐union test or to a test which follows asymptotically a mixture of generalized chi‐squared distributions. They investigate the performance of this asymptotic test and provide an exact modification. They show that this test considerably outperforms multiple testing methods such as the Bonferroni adjustment with respect to power. They illustrate their methods with a cancer study to compare antiemetic agents. Finally, they discuss the extension of the results to other settings, such as Gaussian endpoints.
Theoretical properties of tests for spatial clustering of count data
Authors: Jung Inkyung , Kulldorff Martin 
Published: February 2009

AbstractTesting for spatial clustering of count data is an important problem in spatial data analysis. Several procedures have been proposed to this end but despite their extensive use, studies of their fundamental theoretical properties are almost non‐existent. The authors suggest two conditions that any reasonable test for spatial clustering should satisfy. The latter are based on the notion that the null hypothesis should be rejected almost surely as the amount of spatial clustering tends to infinity. The authors show that the chisquared test and the Potthoff—Whittinghill V have both properties but that other classical tests do not.
Nonresponse weighting adjustment using estimated response probability
Authors: Kim Jae Kwang , Kim Jay J. 
Published: February 2009

AbstractTo reduce nonresponse bias in sample surveys, a method of nonresponse weighting adjustment is often used which consists of multiplying the sampling weight of the respondent by the inverse of the estimated response probability. The authors examine the asymptotic properties of this estimator. They prove that it is generally more efficient than an estimator which uses the true response probability, provided that the parameters which govern this probability are estimated by maximum likelihood. The authors discuss variance estimation methods that account for the effect of using the estimated response probability; they compare their performances in a small simulation study. They also discuss extensions to the regression estimator.
A family of power‐divergence diagnostics for goodness‐of‐fit
Authors: Carota Cinzia 
Published: February 2009

AbstractThe author extends to the Bayesian nonparametric context the multinomial goodness‐of‐fit tests due to Cressie & Read (1984). Her approach is suitable when the model of interest is a discrete distribution. She provides an explicit form for the tests, which are based on power‐divergence measures between a prior Dirichlet process that is highly concentrated around the model of interest and the corresponding posterior Dirichlet process. In addition to providing interesting special cases and useful approximations, she discusses calibration and the choice of test through examples.
Empirical likelihood‐based inference for genetic mixture models
Authors: Huang Chiung‐Yu , Qin Jing , Zou Fei 
Published: February 2009

AbstractThe authors show how the genetic effect of a quantitative trait locus can be estimated by a nonparametric empirical likelihood method when the phenotype distributions are completely unspecified. They use an empirical likelihood ratio statistic for testing the genetic effect and obtaining confidence intervals. In addition to studying the asymptotic properties of these procedures, the authors present simulation results and illustrate their approach with a study on breast cancer resistance genes.
Distribution‐free statistical intervals via ranked‐set sampling
Authors: Frey Jesse 
Published: February 2009

AbstractThe author shows how to construct distribution‐free statistical intervals from ranked‐set sampling. He considers the cases of confidence, tolerance, and prediction intervals. He shows how to compute their coverage probabilities and he compares their performance to that of intervals based on simple random sampling. He finds that the ranked‐set sampling‐based intervals are at least as good as their classical counterpart in most settings of interest, although the nature of the advantage depends on the type of interval considered.
A multivariate von mises distribution with applications to bioinformatics
Authors: Mardia Kanti V. , Hughes Gareth , Taylor Charles C. , Singh Harshinder 
Published: February 2009

AbstractMotivated by problems of modelling torsional angles in molecules, Singh, Hnizdo & Demchuk (2002) proposed a bivariate circular model which is a natural torus analogue of the bivariate normal distribution and a natural extension of the univariate von Mises distribution to the bivariate case. The authors present here a multivariate extension of the bivariate model of Singh, Hnizdo & Demchuk (2002). They study the conditional distributions and investigate the shapes of marginal distributions for a special case. The methods of moments and pseudo‐likelihood are considered for the estimation of parameters of the new distribution. The authors investigate the efficiency of the pseudo‐likelihood approach in three dimensions. They illustrate their methods with protein data of conformational angles
Proportional hazards models based on biased samples and estimated selection probabilities
Authors: Pan Qing , Schaubel Douglas E. 
Published: February 2009

AbstractIn non‐randomized biomedical studies using the proportional hazards model, the data often constitute an unrepresentative sample of the underlying target population, which results in biased regression coefficients. The bias can be avoided by weighting included subjects by the inverse of their respective selection probabilities, as proposed by Horvitz & Thompson (1952) and extended to the proportional hazards setting for use in surveys by Binder (1992) and Lin (2000). In practice, the weights are often estimated and must be treated as such in order for the resulting inference to be accurate. The authors propose a two‐stage weighted proportional hazards model in which, at the first stage, weights are estimated through a logistic regression model fitted to a representative sample from the target population. At the second stage, a weighted Cox model is fitted to the biased sample. The authors propose estimators for the regression parameter and cumulative baseline hazard. They derive the asymptotic properties of the parameter estimators, accounting for the difference in the variance introduced by the randomness of the weights. They evaluate the accuracy of the asymptotic approximations in finite samples through simulation. They illustrate their approach in an analysis of renal transplant patients using data obtained from the Scientific Registry of Transplant Recipients
Testing homogeneity in a mixture of von mises distributions with a structural parameter
Authors: Chen Jiahua , Li Pengfei , Fu Yuejiao 
Published: February 2009

AbstractThe modified likelihood ratio statistic can be used to test the homogeneity in a variety of mixture models. Here, the authors propose the use of the modified and the iterative modified likelihood ratio for testing homogeneity against a two‐component von Mises mixture with a structural parameter. They derive the limiting distributions of the test statistics and propose methods to improve the accuracy of the asymptotic approximation in finite samples. Their simulations show that the tests maintain their nominal level and that they have adequate power. Data on movements of turtles are used as an illustration
Logistic discrimination using robust estimators: An influence function approach
Authors: Croux Christophe , Haesbroeck Gentiane , Joossens Kristel 
Published: February 2009

AbstractLogistic regression is frequently used for classifying observations into two groups. Unfortunately there are often outlying observations in a data set and these might affect the estimated model and the associated classification error rate. In this paper, the authors study the effect of observations in the training sample on the error rate by deriving influence functions. They obtain a general expression for the influence function of the error rate, and they compute it for the maximum likelihood estimator as well as for several robust logistic discrimination procedures. Besides being of interest in their own right, the influence functions are also used to derive asymptotic classification efficiencies of different logistic discrimination rules. The authors also show how influential points can be detected by means of a diagnostic plot based on the values of the influence function
Ranked set sampling for ordered categorical variables
Authors: Chen Haiying , Stasny Elizabeth A. , Wolfe Douglas A. 
Published: February 2009

AbstractThe authors show how ranked set sampling, both balanced and unbalanced, can be extended to ordered categorical variables with the goal of estimating the probabilities of all categories. They use ordinal logistic regression to aid in the ranking of the ordinal variable of interest. They also propose an optimal allocation scheme and methods for implementing it under either perfect or imperfect rankings. Results from a simulation study using data from the third National Health and Nutrition Examination Survey indicate that the use of ordinal logistic regression in ranking leads to substantial gains in precision for estimation of cell probabilities.
Forecasting mortality rates via density ratio modeling
Authors: Kedem Benjamin , Lu Guanhua , Wei Rong , Williams Paul D. 
Published: February 2009

AbstractThe authors propose a semiparametric approach to modeling and forecasting age‐specific mortality in the United States. Their method is based on an extension of a class of semiparametric models to time series. It combines information from several time series and estimates the predictive distribution conditional on past data. The conditional expectation, which is the most commonly used predictor in practice, is the first moment of this distribution. The authors compare their method to that of Lee and Carter.
Testing for lack of dependence in the functional linear model
Authors: Kokoszka Piotr , Maslova Inga , Sojka Jan , Zhu Lie 
Published: February 2009

AbstractThe authors consider the linear model Yn = ψXn + ϵn relating a functional response with explanatory variables. They propose a simple test of the nullity of ψ based on the principal component decomposition. The limiting distribution of their test statistic is chi‐squared, but this distribution is also an excellent approximation in finite samples. The authors illustrate their method using data from terrestrial magnetic observatories.
Local influence in multilevel models
Authors: Shi Lei , Chen Gemai 
Published: February 2009

AbstractThe authors study the local influence of observations in multilevel regression models. To this end, they perturb simultaneously the variances, responses and design matrix. To measure the local change caused by these perturbations, they use generalized Cook statistics for the fixed and random parameter estimates. Closed form local influence measures also allow them to assess the joint influence of various observations. They suggest a simple computation method and illustrate their results using two examples.
Nonparametric test for checking lack of fit of the quantité regression model under random censoring
Authors: Wang Lan 
Published: February 2009

AbstractThe author proposes a nonparametric test for checking the lack of fit of the quantile function of survival time given the covariates; she assumes that survival time is subjected to random right censoring. Her test statistic is a kemel‐based smoothing estimator of a moment condition. The test statistic is asymptotically Gaussian under the null hypothesis. The author investigates its behavior under local alternative sequences. She assesses its finite‐sample power through simulations and illustrates its use with the Stanford heart transplant data.
Outcomes of contemporary Interventional Therapy of ST Elevation Infarction in Patients Older than 75 Years
Authors: Zimmermann Stefan , Ruthrof Susanne , Nowak Kathrin , Klinghammer Lutz , Ludwig Josef , Daniel Werner G. , Flachskampf Frank A. 
Published: February 2009

AbstractBackgroundData on contemporary real‐world outcomes of interventional revascularization in patients ≥ 75 y of age with ST elevation infarction (STEMI) are limited.MethodsWe analyzed all 504 consecutive patients who underwent angiography for acute STEMI between 1999 and 2005 at our center, and followed them up over one year. Outcomes in patients ≥ 75 y of age were compared with younger patients.ResultsPatients ≥ 75 y of age (n = 115) were majority females (55% versus 21%, p < 0.001), more cases of diabetes (42% versus 27%, p = 0.004), hypertension (78% versus 65%, p = 0.03) and a history of coronary events (25% versus 15%, p = 0.002). Younger patients were more often smokers (63% versus 30%, p < 0.001). After coronary angiography patients ≥ 75 y of age underwent less frequent intervention (PCI; 84% versus 93%, p = 0.01). However, if PCI was performed, technical success rates were similar to younger patients (84% versus 86%). The 30‐d mortality was 13% versus 6.4% (p = 0.03), but after successful PCI, the 30‐d mortality rate was not significantly higher in old patients (7.4% versus 3.9%, p = 0.23). Bleeding complications were very low in both age groups if the radial access route was chosen. Multivariate predictors of 30‐d mortality were cardiogenic shock/survived cardiac arrest, ejection fraction < 30%, conservative treatment or unsuccessful PCI (OR 3.01), renal insufficiency, diabetes, and age. One‐y mortality was higher in the elderly (24.3% versus 9.9%, p < 0.001). Among 30‐d‐survivors, only multivessel disease and age were multivariate predictors of 1‐y mortality.ConclusionPatients ≥ 75 y of age benefit from PCI in STEMI, and failed or unattempted PCI worsens prognosis in the old as well as in younger patients. Copyright © 2009 Wiley Periodicals, Inc.
Essential Thrombocythemia: A Case of Acute ST‐Segment Elevation Myocardial Infarction in a Young Female
Authors: Bildirici Ulas , Celikyurt Umut , Ural Ertan 
Published: February 2009

AbstractEssential thrombocythemia (ET) is a clonal disorder of the myeloid stem cell that causes abnormal proliferation of the megakaryocytes. The main feature of the disease is arterial and venous thrombosis caused by platelet dysfunction. Coronary artery involvement leading to acute coronary syndromes is a rare complication of the ET. We report a coronary angioplasty and stenting in a 30‐year‐old female patient with acute ST‐segment elevation myocardial infarction (MI) as the first clinical sign of essential thrombocythemia. Facilitated percutaneous coronary intervention with GPIIb/IIIa and/or thrombolytic therapy may be considered as the first treatment modality for this patient group. Copyright © 2009 Wiley Periodicals, Inc.
Would Different Routine Precordial Electrode Positions Be More Useful? Answer: Not Likely
Authors: Willis Hurst J. 
Published: February 2009

AbstractThere are reasons to wonder if the current precordial electrode positions are the best ones to study the electrical forces of the heart. Theoretically, more horizontal electrode positions and several superior and inferior electrode positions that are perpendicular to the horizontally placed electrode positions should make a superior lead system.A study was designed to determine if that was true.The result of the study indicated that such a system did not solve all of the problems that were posed by the current system. Although the new system was easier to use, the findings did not justify a change from the presently used system of precordial electrode placement. Copyright © 2009 Wiley Periodicals, Inc.
Cardiovascular Studies and the Radiation Dose
Authors: Conti C. Richard 
Published: February 2009

AbstractIn a previous editorial, I commented on ionizing radiation associated with multislice computed tomographic angiography and x‐ray coronary angiography performed in the catheterization laboratory.1 I mentioned that just by living, all of us are exposed to a background radiation dose, probably in the neighborhood of 3.6 millisieverts per year. Copyright © 2009 Wiley Periodicals, Inc.
Extreme Value Analysis of Istanbul Air Pollution Data
Authors: Ercelebi Selamet G. , Toros Hüseyin 
Published: February 2009

AbstractWith respect to air quality standards, extreme events are usually of the most interest. Air quality standards require that the observed extreme concentration in a given time interval must not exceed a certain value. In this paper, it is shown that the measured maximum concentration in a time interval can be represented by one of three types of large asymptotic distribution of extreme value statistics. By using this statistical tool, it is possible to analyze the data and to predict the future extreme concentrations with a given probability. The theoretical background of extreme value statistics, procedure to estimate the parameters of the largest extreme value distributions and procedure to forecast future extreme events are briefly explained. The theory is applied to data obtained from two permanent stations in Istanbul. Hourly SO2 and NO2 concentrations are analyzed and future largest SO2 and NO2 concentrations for the following 12 months are forecasted. It has been found that Gumbel's Type I and Type II extreme value distributions represent these air quality data obtained from the two stations very well. The expected maximum SO2 concentration is found to be 593.7 mg/m3 and the NO2 concentration is found to be 393.4 mg/m3 for the Alibeykoy station. The air quality exceeds the limit of EN standards for hourly SO2 concentration twice a year or in a return period of 5.77 months, and 5 times a year or in a return period of 2.6 months for the hourly NO2 concentrations. Similarly, for the Umraniye station, the expected maximum concentration is 514.5 mg/m3 SO2 with a return period of 1.78 months and 437.6 mg/m3 NO2 with a return period of 5.6 months. The performed prediction suggests that preventive measures should be carried out in the future in order to meet stringent air quality standards.
Prognostic impact of blood transfusion in patients undergoing primary surgery and free‐flap reconstruction for oral squamous cell carcinoma
Authors: Fenner Matthias , Vairaktaris Eleftherios , Nkenke Emeka , Weisbach Volker , Neukam Friedrich W. , Radespiel‐Tröger Martin 
Published: February 2009

AbstractBACKGROUND:The objective of this study was to assess the impact of perioperative transfusion on the prognosis of patients who underwent complete (R0) resection of oral squamous cell carcinoma and reconstruction by microvascular flaps.METHODS:By following an inclusion and exclusion protocol, 223 patients were included in the study who underwent R0 resection of oral squamous cell carcinoma and reconstruction by microvascular flaps at a single center. Clinical and pathologic factors as well as transfusion data were retrieved from a prospective database and analyzed retrospectively. Survival data were assessed using the method of Kaplan and Meier. For multivariate analysis the accelerated failure time model (Weibull distribution) was chosen.RESULTS:The overall survival rate was 71% at 1 year, 67% at 3 years, and 55% at 5 years. In univariate analysis, age (P = .003), tumor size (P = .005), lymph node status (P = .008), tumor differentiation (P = .008), transfusion (P = .006), American Society of Anesthesiologists (ASA) class (P = .001), and mandibular reconstruction (P = .045) were associated significantly with overall survival. Multivariate analysis identified only age, histopathologic differentiation, and ASA class as independent risk factors (P < .001, P = .04, and P = .049, respectively). Age was identified as the strongest independent predictor for overall survival (hazards ratio for each 13‐year increase in age, 1.97; 95% confidence interval, 1.36‐2.85).CONCLUSIONS:Transfusion of >4 U of blood did not appear to influence overall survival in patients who underwent primary surgery for oral squamous cell carcinoma. Because age and ASA class evolved as the strongest predictors of shortened overall survival, associated comorbidities may require more attention, particularly in elderly or socially deprived patients. Cancer 2009. © 2009 American Cancer Society.
Extracellular and intracellular mechanisms that mediate the metastatic activity of exogenous osteopontin
Authors: Mandelin Jami , Lin Emme C. K. , Hu Dana D. , Knowles Susan K. , Do Kim‐Anh , Wang Xuemei , Sage E. Helene , Smith Jeffrey W. , Arap Wadih , Pasqualini Renata 
Published: February 2009

AbstractBACKGROUND:Osteopontin affects several steps of the metastatic cascade. Despite direct correlation with metastasis in experimental systems and in patient studies, the extracellular and intracellular basis for these observations remains unsolved. In this study, the authors used human melanoma and sarcoma cell lines to evaluate the effects of soluble osteopontin on metastasis.METHODS:Exogenous osteopontin or negative controls, including a site‐directed mutant osteopontin, were used in functional assays in vitro, ex vivo, and in vivo that were designed to test the extracellular and intracellular mechanisms involved in experimental metastasis.RESULTS:In the extracellular environment, the results confirmed that soluble osteopontin is required for its prometastatic effects; this phenomenon is specific, arginine‐glycine‐aspartic acid (RGD)‐dependent, and evident in experimental models of metastasis. In the intracellular environment, osteopontin initially induced rapid tyrosine 418 (Tyr‐418) dephosphorylation of the cellular homolog of the Rous sarcoma virus (c‐Src), with decreases in actin stress fibers and increased binding to the vascular endothelium. This heretofore undescribed Tyr dephosphorylation was followed by a tandem c‐Src phosphorylation after tumor cell attachment to the metastatic site.CONCLUSIONS:The results of this study revealed a complex molecular interaction as well as a dual role for osteopontin in metastasis that depends on whether tumor cells are in circulation or attached. Such context‐dependent functional insights may contribute to antimetastasis strategies. Cancer 2009. © 2009 American Cancer Society.