bluuebunny/crossref_metadata_2025_split huggingface dataset:
Omitted variables in longitudinal data models
Authors: Frees Edward W. 
Published: June 2006

AbstractThe omission of important variables is a well‐known model specification issue in regression analysis and mixed linear models. The author considers longitudinal data models that are special cases of the mixed linear models; in particular, they are linear models of repeated observations on a subject. Models of omitted variables have origins in both the econometrics and biostatistics literatures. The author describes regression coefficient estimators that are robust to and that provide the basis for detecting the influence of certain types of omitted variables. New robust estimators and omitted variable tests are introduced and illustrated with a case study that investigates the determinants of tax liability.
Corrigenda: Confidence curves and improved exact confidence intervals for discrete distribution
Authors: Blaker Helge 
Published: June 2006

AbstractDue to a typesetting error, the second sentence in the proof of Theorem 2 on page 792 was garbled. It should read, “It suffices to consider confidence intervals when x = 1 is observed, although this phenomenon always occurs if the rejection regions involve probabilities from both tails.”
The behrens‐fisher problem revisited: A bayes‐frequentist synthesis
Authors: Ghosh Malay , Kim Yeong‐Hwa 
Published: June 2006

AbstractThe Behrens‐Fisher problem concerns the inference for the difference between the means of two normal populations whose ratio of variances is unknown. In this situation, Fisher's fiducial interval differs markedly from the Neyman‐Pearson confidence interval. A prior proposed by Jeffreys leads to a credible interval that is equivalent to Fisher's solution but it carries a different interpretation. The authors propose an alternative prior leading to a credible interval whose asymptotic coverage probability matches the frequentist coverage probability more accurately than the interval of Jeffreys. Their simulation results indicate excellent matching even in small samples.
Probability matching priors for an extended statistical calibration model
Authors: Eno Daniel R. , Ye Keying 
Published: June 2006

AbstractStatistical calibration or inverse prediction involves data collected in two stages. In the first stage, several values of an endogenous variable are observed, each corresponding to a known value of an exogenous variable; in the second stage, one or more values of the endogenous variable are observed which correspond to an unknown value of the exogenous variable. When estimating the value of the latter, it has been suggested that the variability about the regression relationship should not be assumed to be equal for the two stages of data collection. In this paper, the authors present a Bayesian method of analysis based on noninformative priors that takes this heteroscedasticity into account.
Evaluating fit in functional data analysis using model embeddings
Authors: Viele Kert 
Published: June 2006

AbstractThe author proposes a general method for evaluating the fit of a model for functional data. His approach consists of embedding the proposed model into a larger family of models, assuming the true process generating the data is within the larger family, and then computing a posterior distribution for the Kullback‐Leibler distance between the true and the proposed models. The technique is illustrated on biomechanical data reported by Ramsay, Flanagan & Wang (1995). It is developed in detail for hierarchical polynomial models such as those found in Lindley & Smith (1972), and is also generally applicable to longitudinal data analysis where polynomials are fit to many individuals.
Simple and accurate one‐sided inference from signed roots of likelihood ratios
Authors: Diciccio Thomas J. , Martin Michael A. , Stern Steven E. 
Published: June 2006

AbstractThe authors propose two methods based on the signed root of the likelihood ratio statistic for one‐sided testing of a simple null hypothesis about a scalar parameter in the présence of nuisance parameters. Both methods are third‐order accurate and utilise simulation to avoid the need for onerous analytical calculations characteristic of competing saddlepoint procedures. Moreover, the new methods do not require specification of ancillary statistics. The methods respect the conditioning associated with similar tests up to an error of third order, and conditioning on ancillary statistics to an error of second order.
Projection de hájek et polynômes de bernstein
Authors: Hallin Marc , Mellouk Amal , Rifi Khalid 
Published: June 2006

AbstractLes auteurs établissent la forme explicite, sous l'hypothèse de bruit blanc, de la représentation asymptotique fournie (sous forme non explicite) par le célèbre lemme de projection de Hájek (1968) pour les statistiques de rangs linéaires dans le cas des scores dits approchés. Fondée sur les polynômes de Bernstein, cette représentation est meilleure, au sens de la norme quadratique, que celle de Hájek (1961, 1962) qui est habituellement considérée. Cette représentation polynomiale permet de redémontrer les résultats classiques (normalité asymptotique et borne de Berry‐Esséen). Les simulations indiquent, par ailleurs, que la qualité de l'approximation fournie est significativement meilleure, pour les échantillons de taille finie, que celle qui résulte de la représentation traditionnelle.
The likelihood ratio test for homogeneity in finite mixture models
Authors: Chen Hanfeng , Chen Jiahua 
Published: June 2006

AbstractThe authors study the asymptotic behaviour of the likelihood ratio statistic for testing homogeneity in the finite mixture models of a general parametric distribution family. They prove that the limiting distribution of this statistic is the squared supremum of a truncated standard Gaussian process. The autocorrelation function of the Gaussian process is explicitly presented. A re‐sampling procedure is recommended to obtain the asymptotic p‐value. Three kernel functions, normal, binomial and Poisson, are used in a simulation study which illustrates the procedure.
Asymptotics for L1‐estimators of regression parameters under heteroscedasticityY
Authors: Knight Keith 
Published: June 2006

AbstractWe consider the asymptotic behaviour of L1 ‐estimators in a linear regression under a very general form of heteroscedasticity. The limiting distributions of the estimators are derived under standard conditions on the design. We also consider the asymptotic behaviour of the bootstrap in the heteroscedastic model and show that it is consistent to first order only if the limiting distribution is normal.
Robust inference for bivariate point processes
Authors: Ng Edmund T. M. , Cook Richard J. 
Published: June 2006

AbstractIn the analysis of recurrent events where the primary interest lies in studying covariate effects on the expected number of events occurring over a period of time, it is appealing to base models on the cumulative mean function (CMF) of the processes (Lawless & Nadeau 1995). In many chronic diseases, however, more than one type of event is manifested. Here we develop a robust inference procedure for joint regression models for the CMFs arising from a bivariate point process. Consistent parameter estimates with robust variance estimates are obtained via unbiased estimating functions for the CMFs. In most situations, the covariance structure of the bivariate point processes is difficult to specify correctly, but when it is known, an optimal estimating function for the CMFs can be obtained. As a convenient model for more general settings, we suggest the use of the estimating functions arising from bivariate mixed Poisson processes. Simulation studies demonstrate that the estimators based on this working model are practically unbiased with robust variance estimates. Furthermore, hypothesis tests may be based on the generalized Wald or generalized score tests. Data from a trial of patients with bronchial asthma are analyzed to illustrate the estimation and inference procedures.
A prior for the variance in hierarchical models
Authors: Daniels Michael J. 
Published: June 2006

AbstractThe choice of prior distributions for the variances can be important and quite difficult in Bayesian hierarchical and variance component models. For situations where little prior information is available, a ‘nonin‐formative’ type prior is usually chosen. ‘Noninformative’ priors have been discussed by many authors and used in many contexts. However, care must be taken using these prior distributions as many are improper and thus, can lead to improper posterior distributions. Additionally, in small samples, these priors can be ‘informative’. In this paper, we investigate a proper ‘vague’ prior, the uniform shrinkage prior (Strawder‐man 1971; Christiansen & Morris 1997). We discuss its properties and show how posterior distributions for common hierarchical models using this prior lead to proper posterior distributions. We also illustrate the attractive frequentist properties of this prior for a normal hierarchical model including testing and estimation. To conclude, we generalize this prior to the multivariate situation of a covariance matrix.
On maximum likelihood estimation of the binomial parameter n
Authors: Gupta A. K. , Nguyen T. T. , Wang Yining 
Published: June 2006

AbstractThis paper gives a necessary and sufficient condition for the existence of a finite conditional maximum‐likelihood estimate for the binomial parameter n. Upper bounds for the conditional and beta‐binomial maximum‐likelihood estimators are derived. An example is given to show that the conditional likelihood function and the beta‐binomial likelihood function may not be unimodal.
A generalized‐moments specification test for the logistic link
Authors: Fokianos Konstantinos , Peng Amy , Qin Jing 
Published: June 2006

AbstractThe authors consider the problem of testing the validity of the logistic regression model using a random sample. Given the values of the response variable, they observe that the sample actually consists of two independent subsets of observations whose density ratio has a known parametric form when the model is true. They are thus led to propose a generalized‐moments specification test in detail. In addition, they show that this test can be derived using Neyman's smooth tests for goodness of fit. They present simulation results and apply the methodology to the analysis of two real data sets.
Minimax designs for approximately linear models with AR(1) errors
Authors: Wiens Douglas P. , Zohu Julie 
Published: June 2006

AbstractWe obtain designs for linear regression models under two main departures from the classical assumptions: (1) the response is taken to be onlyapproximatelylinear, and (2) the errors are not assumed to be independent, but to instead follow a first‐order autoregressive process. These designs have the property that they minimize (a modification of) the maximum integrated mean squared error of the estimated response, with the maximum taken over a class of departures from strict linearity and over all autoregression parameters ρ,|ρ,| < 1, of fixed sign. Specific methods of implementation are discussed. We find that an asymptotically optimal procedure for AR(1) models consists of choosing points from that design measure which is optimal for uncorrelated errors, and then implementing them in an appropriate order.
The weighted likelihood
Authors: Hu Feifang , Zidek James V. 
Published: June 2006

AbstractThe authors consider a weighted version of the classical likelihood that applies when the need is felt to diminish the role of some of the data in order to trade bias for precision. They propose an axiomatic derivation of the weighted likelihood, for which they show that aspects of classical theory continue to obtain. They suggest a data‐based method of selecting the weights and show that it leads to the James‐Stein estimator in various contexts. They also provide applications.
Score tests for heterogeneity and overdispersion in zero‐inflated Poisson and binomial regression models
Authors: Hall Daniel B. , Berenhaut Kenneth S. 
Published: June 2006

AbstractHall (2000) has described zero‐inflated Poisson and binomial regression models that include random effects to account for excess zeros and additional sources of heterogeneity in the data. The authors of the present paper propose a general score test for the null hypothesis that variance components associated with these random effects are zero. For a zero‐inflated Poisson model with random intercept, the new test reduces to an alternative to the overdispersion test of Ridout, Demério & Hinde (2001). The authors also examine their general test in the special case of the zero‐inflated binomial model with random intercept and propose an overdispersion test in that context which is based on a beta‐binomial alternative.
A dual tyrosine‐leucine motif mediates myelin protein P0 targeting in MDCK cells
Authors: Kidd Grahame J. , Yadav Vijay K. , Huang Ping , Brand Stacey L. , Low Seng Hui , Weimbs Thomas , Trapp Bruce D. 
Published: June 2006

AbstractDifferential targeting of myelin proteins to multiple, biochemically and functionally distinct Schwann cell plasma membrane domains is essential for myelin formation. In this study, we investigated whether the myelin protein P0 contains targeting signals using Madin‐Darby canine kidney (MDCK) cells. By confocal microscopy, P0 was localized to MDCK cell basolateral membranes. C‐terminal deletion resulted in apical accumulation, and stepwise deletions defined a 15‐mer region that was required for basolateral targeting. Alanine substitutions within this region identified the YAML sequence as a functional tyrosine‐based targeting signal, with the ML sequence serving as a secondary leucine‐based signal. Replacement of the P0 ectodomain with green fluorescent protein altered the distribution of constructs lacking the YAML signal. Coexpression of the myelin‐associated glycoprotein did not alter P0 distribution in MDCK cells. The results indicate that P0 contains a hierarchy of targeting signals, which may contribute to P0 localization in myelinating Schwann cells and the pathogenesis in human disease. © 2006 Wiley‐Liss, Inc.
Survival and differentiation of embryonic neural explants on different biomaterials
Authors: Soria José Miguel , Martínez Ramos Cristina , Salmerón Sánchez Manuel , Benavent Veronique , Campillo Fernández Alberto , Gómez Ribelles José Luis , García Verdugo José Manuel , Pradas Manuel Monleón , Barcia Juan Antonio 
Published: June 2006

AbstractBiomaterials prepared from polyacrylamide, ethyl acrylate (EA), and hydroxyethyl acrylate (HEA) in various blend ratios, methyl acrylate and chitosan, were tested in vitro as culture substrates and compared for their ability to be colonized by the cells migrating from embryonic brain explants. Neural explants were isolated from proliferative areas of the medial ganglionic eminence and the cortical ventricular zone of embryonic rat brains and cultured in vitro on the different biomaterials. Chitosan, poly(methyl acrylate), and the 50% wt copolymer of EA and HEA were the most suitable substrates to promote cell attachment and differentiation of the neural cells among those tested. Immunofluorescence microscopy analysis showed that progenitor cells had undergone differentiation and that the resulting glial and neuronal cells expressed their intrinsic morphological characteristics in culture. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006
Closing capacity of cranial bone defects using porous calcium phosphate cement implants in a rabbit animal model
Authors: Kroese‐Deutman H.C. , Wolke J.G.C. , Spauwen P.H.M. , Jansen J.A. 
Published: June 2006

AbstractCalcium phosphate (Ca‐P) cement is a well established material for bone repair. The bone biological properties of Ca‐P cement can even be further improved by creating porosity in the material. The current study aimed on the evaluation of the osteoconductive behavior of porous Ca‐P cement. Therefore, circular defects (6, 9, and 15 mm in diameter) were created in the cranium of 3 months old rabbits and filled with porous Ca‐P cement implants. The total porosity of implants was calculated to be 71, 74 and 74% respectively and the average pore diameter was 150 μm. In addition, empty control defects were prepared. After 12 weeks implantation time the animals were sacrificed and radiographic, histological, and histomorphometrical evaluation was performed. The Critical Size Defect (CSD) of this species at this location for an implantation time of 12 weeks was confirmed to be 15 mm. Bone was observed to be present over and through almost all porous Ca‐P cement implants. Only, in one out of eight animals with a 15 mm implant complete bone bridging of the defect did not occur. The size of the defect was found not to affect the total percentage of bone formation in the cement; (17 ± 7)%, (18 ± 6)% and (17 ± 3)% for respectively 6, 9, and 15 mm diameter implants. We concluded that porous Ca‐P cement is an excellent osteoconductive material in non weight bearing situations and complete bridging of a critical sized skull defect occurs in this rabbit model after 12 weeks of implantation. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006
Micromolding of photocrosslinkable hyaluronic acid for cell encapsulation and entrapment
Authors: Khademhosseini Ali , Eng George , Yeh Judy , Fukuda Junji , Blumling James , Langer Robert , Burdick Jason A. 
Published: June 2006

AbstractMicropatterning of hydrogels is potentially useful for a variety of applications, including tissue engineering, fundamental biological studies, diagnostics, and high‐throughput screening. Although synthetic polymers have been developed for these applications, natural polymers such as polysaccharides may have advantages for biological samples and cell‐based devices because they are natural components of the in vivo microenvironment. In this study, we synthesized and used hyaluronic acid (HA) modified with photoreactive methacrylates to fabricate microstructures as functional components of microfabricated devices. To demonstrate the universality of this approach, two types of microstructures were formed. In the first approach, HA microstructures were fabricated and used as docking templates to enable the subsequent formation of cell microarrays within low shear stress regions of the patterns. Cells within these microwells remained viable, could generate spheroids, and could be retrieved using mechanical disruption. In the second approach, cells were encapsulated directly within the HA hydrogels. Arrays of viable embryonic stem (ES) cells or fibroblasts were encapsulated within HA hydrogels and could later be recovered using enzymatic digestion of the microstructures. These results demonstrate that it is possible to incorporate photocrosslinkable HA, a natural, versatile, degradable, and biocompatible biopolymer, into micro‐electromechanical systems. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006
Localization of CYP4B1 in the rat nasal cavity and analysis of CYPs as secreted proteins
Authors: Genter Mary Beth , Yost Garold S. , Rettie Allan E. 
Published: June 2006

AbstractCYP4B1 is highly expressed in rat nasal respiratory mucosa, and to a lesser extent in olfactory mucosa. Examination of high‐power photomicrographs suggests that CYP4B1 may be a secreted protein, based on the fact that immunoreactivity appears to be present in the lumens of ducts of Bowman's glands (rather than intracellular localization, as we observed with an antibody recognizing CYP2F4) and in secretory granules in respiratory mucosa. Furthermore, anti‐CYP4B1 immunoreactivity is present on the surface of both respiratory and olfactory mucosa. We used SignalP 3.0 analysis to ascertain the likelihood that rat CYP4B1 is a secreted protein. While this analysis does not suggest that rat CYP4B1 is a secreted protein, several other cytochrome P450 enzymes were predicted to be secreted proteins. The observation that multiple human cytochrome P450s appear to be secreted proteins helps to explain the appearance of anti‐cytochrome P450 antigens in cases of human autoimmune liver diseases. © 2006 Wiley Periodicals, Inc. J Biochem Mol Toxicol 20:139–141, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20123
The effect of intron location on the splicing of BmKK2 in 293T cells
Authors: Zhijian Cao , Chao Dai , Dahe Jiang , Wenxin Li 
Published: June 2006

AbstractPreviously reported results showed that the BmKK2's intron could be recognized and spliced in cultured HEK 293T cells. At the same time, a cryptic splicing site of BmKK2 gene was found in the second exon. Moreover, replacing BmKK2's intron with BmP03's intron (an artificial BmKK2‐BmP03 mosaic gene) did not affect the intron's recognition and splicing, but increased the expression level of the toxin‐GFP fusion protein (Cao et al., J Biochem Mol Toxicol 2006;20:1–6). In this investigation, the BmKK2's intron with 79 nucleotides length was artificially shifted from the 49th nt (the 17th Gly codon between the first base and the second base) to the 100th nt (the 34th Gly codon between the first base and the second base). Based on the constructed intron‐splicing system, the results of RT‐PCR and the western blotting analysis showed that the BmKK2's shifted‐intron (named BmKK2‐s) was not recognized and spliced correctly, but the cryptic splicing site of BmKK2 gene was still spliced in the second exon, which possibly indicated that locations of introns were very important to the recognition and splicing of introns, and splicing of introns was very much associated with the corresponding upstream and downstream exons. This result possibly provides evidence for splice‐site recognition across the exons. © 2006 Wiley Periodicals, Inc. J Biochem Mol Toxicol 20:127–132, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20127
In vivo molecular imaging of adenoviral versus lentiviral gene therapy in two bone formation models
Authors: Feeley Brian T. , Conduah Augustine H. , Sugiyama Osamu , Krenek Lucie , Chen Irvin S. Y. , Lieberman Jay R. 
Published: June 2006

AbstractRegional gene therapy techniques are promising methods to enhance bone formation in large bone defects that would be difficult to treat with allograft or autograft bone stock. In this study, we compared in vivo temporal expression patterns of adenoviral‐ and lentiviral‐mediated gene therapy in two bone formation models. Primary rat bone marrow cells (RBMC) were transduced with lentiviral or adenoviral vectors containing luciferase (Luc) or BMP‐2 cDNA, or cotransduced with vectors containing Luc and bone morphogenetic protein 2 (BMP‐2). In vitro protein production was determined with luciferase assay or ELISA (for BMP‐2 production) weekly for 12 weeks. Two bone formation models were used—a hind limb muscle pouch or radial defect—in SCID mice. A cooled charged‐coupled device (CCD) camera was used to image in vivo luciferase expression weekly for 12 weeks. In vitro, adenoviral expression of BMP‐2 and luciferase was detected by ELISA or luciferase assay, respectively, for 4 weeks. Lentiviral expression of BMP‐2 and luciferase was sustained in culture for 3 months. Using the CCD camera, we found that adenoviral vectors expressed luciferase expression for up to 21 days, but lentiviral vectors expressed target gene expression for 3 months in vivo in both bone formation models. There was no detectable difference in the amount of bone formed between the adenoviral and lentiviral groups. Lentiviral‐mediated delivery of BMP‐2 can induce long term in vitro and in vivo gene expression, which may be beneficial when developing tissue engineering strategies to heal large bone defects or defects with a compromised biologic environment. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:1709–1721, 2006