bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bayesian estimates of disease maps: How important are priors?
Authors: Bernardinelli L , Clayton D. , Montomoli C. 
Published: April 2007

AbstractIn the fully Bayesian (FB) approach to disease mapping the choice of the hyperprior distribution of the dispersion parameter is a key issue. In this context we investigated the sensitivity of the rate ratio estimates to the choice of the hyperprior via a simulation study. We also compared the performance of the FB approach to mapping disease risk to the conventional approach of mapping maximum likelihood (ML) estimates andp‐values. The study was modelled on the incidence data of insulin dependent diabetes mellitus (IDDM) as observed in the communes of Sardinia.
Bayesian analysis of space—time variation in disease risk
Authors: Bernardinelli L. , Clayton D. , Pascutto C. , Montomoli C. , Ghislandi M. , Songini M. 
Published: April 2007

AbstractThe analysis of variation of risk for a given disease in space and time is a key issue in descriptive epidemiology. When the data are scarce, maximum likelihood estimates of the area‐specific risk and of its linear time‐trend can be seriously affected by random variation. In this paper, we propose a Bayesian model in which both area‐specific intercept and trend are modelled as random effects and correlation between them is allowed for. This model is an extension of that originally proposed for disease mapping. It is illustrated by the analysis of the cumulative prevalence of insulin dependent diabetes mellitus as observed at the military examination of 18‐year‐old conscripts born in Sardinia during the period 1936–1971. Data concerning the genetic differentiation of the Sardinian population are used to interpret the results.
Spatial variation of natural radiation and childhood leukaemia incidence in Great Britain
Authors: Richardson Sylvia , Monfort Christine , Green Martyn , Draper Gerald , Muirhead Colin 
Published: April 2007

AbstractThis paper describes an analysis of the geographical variation of childhood leukaemia incidence in Great Britain over a 15 year period in relation to natural radiation (gamma and radon). Data at the level of the 459 district level local authorities in England, Wales and regional districts in Scotland are analysed in two complementary ways: first, by Poisson regressions with the inclusion of environmental covariates and a smooth spatial structure; secondly, by a hierarchical Bayesian model in which extra‐Poisson variability is modelled explicitly in terms of spatial and non‐spatial components. From this analysis, we deduce a strong indication that a main part of the variability is accounted for by a local neighbourhood ‘clustering’ structure. This structure is furthermore relatively stable over the 15 year period for the lymphocytic leukaemias which make up the majority of observed cases. We found no evidence of a positive association of childhood leukaemia incidence with outdoor or indoor gamma radiation levels. There is no consistent evidence of any association with radon levels. Indeed, in the Poisson regressions, a significant positive association was only observed for one 5‐year period, a result which is not compatible with a stable environmental effect. Moreover, this positive association became clearly non‐significant when over‐dispersion relative to the Poisson distribution was taken into account.
A Bayesian analysis of bivariate survival data from a multicentre cancer clinical trial
Authors: Gustafson Paul 
Published: April 2007

AbstractI present an analysis of data from a clinical trial of new chemotherapies for colorectal cancer. I model participating clinical sites via random effects, to allow for heterogeneous patient responses across centres. Patient response is measured by both progression and survival times. The data suggest that patient responses are homogeneous before, but heterogeneous after, disease progression. For one new therapy, an increase in efficacy relative to standard therapy is detected before, but not after, progression.
A new approach to selection and weighting of items in evaluative composite measurement scales
Authors: Coste Joël , Walter Eric , Venot Alain 
Published: April 2007

AbstractEvaluative composite measurement scales (CMS) are increasingly used in medicine to measure complex constructs in the absence of a reference criterion or ‘gold standard’. However, the level of measurement provided by these instruments has usually been given little attention. This paper explores the influence of the characteristics of the item set and weighting on the level of measurment of an evaluative CMS. The approach is illustrated with an application to the scoring system of the Nottingham Health Profile. Simulations are provided to indicate when the composite score of item responses, on an ordinal or pass—fail scale, could be considered to achieve the properties of an interval scale.
Determining the value of additional surrogate exposure data for improving the estimate of an odds ratio
Authors: Dahm P. Fred , Gail Mitchel H. , Rosenberg Philip S. , Pee David 
Published: April 2007

AbstractWe consider the design of both cohort and case‐control studies in which an initial (‘stage 1’) sample of complete data on an error‐free disease indicator (D), a correct (‘gold‐standard’) dichotomous exposure measurement (X) and an error‐prone exposure measurement (Z) are available. We calculate the amount of additional information on the odds ratio relating D to X that one can obtain from a second (‘stage 2’) sample of measurements only on D and Z. If one allows for differential measurement error in Z, there is often little advantage in having more than four times as much data in stage 2 data as in stage 1. With the assumption that a non‐differential measurement error model is reasonable, larger amounts of stage 2 data can be useful. Simulations indicate that stage 1 samples of modest size (50 cases in case‐control studies and 50 failures in cohort studies) yield sufficiently reliable estimates of needed parameters to assist in determining an appropriate size for the stage 2 sample. These ideas apply in settings either where the amount of stage 1 data is limited and fixed by external constraints or where one has gathered stage 1 data in advance to avoid collecting superfluous stage 2 data.
Using a mixture model to predict the occurrence of diabetic retinopathy
Authors: Young Philip , Morgan Byron , Sonksen Peter , Till Sebastian , Williams Charles 
Published: April 2007

AbstractDiabetes mellitus is a common condition which has several serious complications associated with it. In this paper a mixture model, based on one previously used to predict the onset of AIDS, is used to predict the onset of one of these complications, diabetic retinopathy, the major cause of adult blindness in the U.K. This model differs from the previous AIDS model by introducing covariates into the model and using a wider choice of mixture distributions. The fit and distributional assumptions of the model are then discussed for this example. The model is fitted to the data by maximum likelihood. It is important that the training set contains balanced numbers of individuals with and without retinopathy.
Optimal and practicable designs for measuring plaque pH‐profiles
Authors: Fedorov V. V. , Hackl P. , Müller W. G. 
Published: April 2007

AbstractThe shape of the plaque pH‐profile after consumption of a food item determines the food's potential caries risk. This and related facts have caused an increased interest in measurements of plaque pH‐profiles during the last decade. A standard design for these measurements is to take equally spaced observations over a certain period of time. The theory of optimal experimental design gives methods for positioning the measurements of a pH‐profile in an optimized way. The objective is to minimize the effort given a desired precision of the estimated profile characteristics or to maximize the precision given the number of measurements. We show that a reduction in the number of measurements up to 50 per cent or a respective improvement in precision of the estimates as compared to standardly applied designs is possible. This implies less inconvenience for the subjects and better compliance with the needs of investigation. Our study is intended to demonstrate the applicability of the theory of optimal experimental design which has the potential to improve the efficiency of medical research.
Validity of the recording of ischaemic heart disease and chronic obstructive pulmonary disease in the Saskatchewan health care datafiles
Authors: Rawson Nigel S. B. , Malcolm Edith 
Published: April 2007

AbstractThe internal validity of the recording of information about ischaemic heart disease (IHD) and chronic obstructive pulmonary disease (COPD) in the administrative health care datafiles of the Canadian province of Saskatchewan is investigated. Comparisons between hospital data and medical charts for acute myocardial infarction and chronic airways obstruction patients showed excellent diagnostic agreement: 97 per cent and 94 per cent, respectively. Appropriate physician service claims were identified for 89 per cent of hospitalizations for IHD and COPD and exact concordance between diagnoses in the two datafiles varied between 15 per cent for acute/sub‐acute IHD and 80 per cent for asthma; including any physician diagnosis within the same broad category (IHD or COPD) increased concordance to 79–94 per cent for IHD and 64–88 per cent for COPD. Contextual information related to the hospitalizations was clinically and epidemiologically realistic.
A personal view of some controversies in allocating treatment to patients in clinical trials
Authors: Senn Stephen 
Published: April 2007

AbstractA non‐exhaustive but nevertheless wide‐ranging if biased and personal view of various matters affecting the allocation of treatments to patients in controlled clinical trials will be undertaken from the standpoint of a statistician working in drug development. The following topics are considered: the use of ‘placebos’ in the run‐in phase; the use of crossover trials; selection of patients; various matters concerning centres; two extreme alternatives to randomization, and various matters linking blinding and allocation.
Effect of non‐random missing data mechanisms in clinical trials
Authors: Choi S. C. , Lu I. L. 
Published: April 2007

AbstractA simple form of non‐ignorable missing data mechanisms based on two parameters is used to characterize the amount of missing data and the severity of non‐randomness in clinical trials. Based on the formulation, the effect of non‐randomly missing data on simple analyses which ignore the missing data is studied for binary and normally distributed response variables. In general, the effect of the non‐randomly missing data on the bias and the power increases with the severity of non‐randomness. The bias can be positive or negative and the power can be less than or greater than when the data are missing at random. The results of the analysis, ignoring the missing data, can be seriously flawed if the non‐randomness is severe, even when only a small proportion of the sample is missing. The problem is more pronounced in the case of normally distributed response variables with unequal variances.
Bayesian approaches to random‐effects meta‐analysis: A comparative study
Authors: Smith Teresa C. , Spiegelhalter David J. , Thomas Andrew 
Published: April 2007

AbstractCurrent methods for meta‐analysis still leave a number of unresolved issues, such as the choice between fixed‐ and random‐effects models, the choice of population distribution in a random‐effects analysis, the treatment of small studies and extreme results, and incorporation of study‐specific covariates. We describe how a full Bayesian analysis can deal with these and other issues in a natural way, illustrated by a recent published example that displays a number of problems. Such analyses are now generally available using the BUGS implementation of Markov chain Monte Carlo numerical integration techniques. Appropriate proper prior distributions are derived, and sensitivity analysis to a variety of prior assumptions carried out. Current methods are briefly summarized and compared to the full Bayes analysis.
Non‐parametric estimation of the post‐lead‐time survival distribution of screen‐detected cancer cases
Authors: Xu Jian‐Lun , Prorok Philip C. 
Published: April 2007

AbstractThe goal of screening programmes for cancer is early detection and treatment with a consequent reduction in mortality from the disease. Screening programmes need to assess the true benefit of screening, that is, the length of time of extension of survival beyond the time of advancement of diagnosis (lead‐time). This paper presents a non‐parametric method to estimate the survival function of the post‐lead‐time survival (or extra survival time) of screen‐detected cancer cases based on the observed total life time, namely, the sum of the lead‐time and the extra survival time. We apply the method to the well‐known data set of the HIP (Health Insurance Plan of Greater New York) breast cancer screening study. We make comparisons with the survival of other groups of cancer cases not detected by screening such as interval cases, cases among individuals who refused screening, and randomized control cases. As compared with Walter and Stitt's model, in which they made parametric assumptions for the extra survival time, our non‐parametric method provides a better fit to HIP data in the sense that our estimator for the total survival time has a smaller sum of squares of residuals.
Disentangling compensation and employment risks using the behavioral agency model
Authors: Larraza‐Kintana Martin , Wiseman Robert M. , Gomez‐Mejia Luis R. , Welbourne Theresa M. 
Published: May 2007

AbstractEmploying survey and archival data from a sample of IPO firms, and extending the ideas of the Behavioral Agency Model, this study examines the influence of various forms of risk bearing created within the compensation contract on perceived risk taking. The results show that employment risk and variability in compensation each corresponds to greater risk taking, while downside risk and the intrinsic value of stock options correspond to lower risk taking. Among the implications from these results are the importance CEOs attach to relatively stable forms of pay, and to drawing distinctions between the potential for loss of pay and uncertainty about the amount of future pay. Copyright © 2007 John Wiley & Sons, Ltd.
The Influence of Environment on Starch Content and Amylose to Amylopectin Ratio in Wheat
Authors: Labuschagne Maryke T. , Geleta Nemera , Osthoff Garry 
Published: May 2007

AbstractThere is evidence that starch content plays an active role in determining dough rheological characteristics. The aim of this study was to determine the influence of environment on starch content and amylose: amylopectin ratio, and how this affects breadmaking quality. Ten hard red spring wheat cultivars were planted in three different environments in a randomized complete block design with three replications. Total starch content, amylose: amylopectin ratio, milling, rheological and baking characteristics were measured. Starch content was significantly influenced by the environment. It was significantly negatively correlated with loaf volume, wet gluten content and flour protein content across the three environments. Starch content and protein content were significantly negatively correlated, yet the value was relatively small (r = −0.4) and the relationship was therefore not directly inverse, and other factors influenced this relationship. Some cultivars interacted with specific environments, and they ranked high for starch content and loaf volume. Amylose: amylopectin ratio was very consistent for the three environments but was not significantly correlated with breadmaking quality characteristics across the environments, although there were significant correlations at individual environments. Cultivar choice and environment where cultivars are planted will therefore affect the starch content. High starch content will not necessarily lead to poor baking quality.
Mechanical properties of (ethylene acrylate copolymer)‐modified polypropylene/TiO2 blends
Authors: Fan Xiyun S. 
Published: May 2007

AbstractAn ethylene‐(methyl acrylate) (EMA) copolymer produced from a tubular reactor was found to be effective in toughening polypropylene, even at low concentrations. The addition of a small amount of TiO2 pigment enhanced the EMA toughening effect. Microscopy and thermal analysis helped to reveal the possible EMA toughening mechanisms. The effects of two processing methods, dry blending and melt blending, on the mechanical properties of the formulation were also studied. J. VINYL ADDIT. TECHNOL., 13:65–70, 2007. © 2007 Society of Plastics Engineers.
Investigation of electrically conductive acrylonitrile‐butadiene rubber
Authors: Kim In 
Published: May 2007

AbstractElectrically conductive acrylonitrile‐butadiene rubbers (NBRs) containing carbon black (CB) as conductive filler were prepared in order to investigate their electrical and mechanical properties. The effects of conductive CB loading, temperature, acrylonitrile content, crosslinking density of vulcanizates, and plasticizer on conductivity were studied. The change in electrical conductivity of NBRs with different amounts of CB showed that there is a certain critical point (percolation threshold) where a significant decrease in electrical resistivity (increase in conductivity) is observed. Mechanical properties such as tensile strength, elongation to break, and surface hardness of vulcanized NBRs were measured. It was found that the percolation threshold was 5 phr of CB for the NBR/CB composites. J. VINYL ADDIT. TECHNOL., 13:71–75, 2007. © 2007 Society of Plastics Engineers.
Mechanical and heat deflection properties of PVC/PMMA/montmorillonite composites
Authors: Pagé D.J.Y.S. , Cunningham N. , Chan N. , Carran G. , Kim J. 
Published: May 2007

AbstractComposites based on PVC were compounded with 5% of montmorillonite and 10% of PMMA. Two types of reinforcement were studied, which included a purified sodium montmorillonite and a montmorillonite organically modified with an alkylammonium chloride. The composites were compounded with a Gelimat type thermokinetic mixer and were ejected at a maximum temperature of 180°C. The organically modified montmorillonite discolored the PVC, result which was interpreted as a sign of chemical degradation caused by the alkylammonium modifier. The composite made with 5% of purified montmorillonite and 10 of % PMMA displayed the best overall properties. The most important improvement was obtained on flexural strain at break (0.097–0.175 mm/mm) and maximum flexural strength (62–76 MPa). The HDT increased by up to 8°C. Dynamic mechanical analysis showed that 10% of PMMA in PVC moved the tan δ peak to temperatures 5–6°C higher. The PMMA was completely miscible in PVC and played an important role in the montmorillonite dispersion, as observed by XRD and SEM analysis. It also contributed to the overall increase in properties of PVC/PMMA/montmorillonite composites. J. VINYL ADDIT. TECHNOL., 13:91–97, 2007. © 2007 Society of Plastics Engineers.
Effect of precipitated calcium carbonate on the mechanical properties of poly(vinyl chloride)
Authors: Fernando N. A. S. , Thomas N. L. 
Published: May 2007

AbstractThis study examines the effect of various grades of precipitated and ground calcium carbonate on the tensile strength and Charpy impact energy of extruded PVC profile. The results confirm that ultra‐fine precipitated calcium carbonate (pcc) can give rise to large improvements in single notch impact strengths. Control values of 9 kJ/m−2 were increased to 79 kJ/m−2 through the addition of ultra‐fine pcc. The results have been interpreted in terms of the particle size, shape, and coating of the calcium carbonate grades and the effect on the gelation characteristics of the PVC formulations. J. VINYL ADDIT. TECHNOL., 13:98–102, 2007. © 2007 Society of Plastics Engineers.
Paracrine effects of direct intramyocardial implantation of bone marrow derived cells to enhance neovascularization in chronic ischaemic myocardium
Authors: Tse Hung‐Fat , Siu Chung‐Wah , Zhu Shu‐Guang , Songyan Liao , Zhang Qing‐Yong , Lai Wing‐Hon , Kwong Yok‐Lam , Nicholls John , Lau Chu‐Pak 
Published: May 2007

AbstractObjectiveTo determine the optimal bone marrow (BM) cell types, and their potential mechanisms of action for neovascularization in chronic ischaemic myocardium.Methods and resultsThe functional effects, angiogenic potential and cytokine expression of direct intramyocardial implantation of autologous BM CD31‐positive endothelial progenitor cells (EPC, n=9), BM mononuclear cells (MNCs, n=9), and saline (n=9) were compared in a swine model of chronic ischaemic myocardium. Autologous BM cells were harvested and catheter‐based electromechanical mapping‐guided direct intramyocardial injection was performed to target ischaemic myocardium. After 12 weeks, injection of BM‐MNC resulted in significant improvements in left ventricular dP/dt (+21±8%, P=0.032), left ventricular pressure (+17±4%, P=0.048) and regional microsphere myocardial perfusion over ischaemic endocardium (+74±28%, P<0.05) and epicardium (+73±29%, P<0.05). No significant effects were observed following injection of BM‐EPC or saline. Capillary density (1132±69 versus 903±44 per mm2, P=0.047) and expression of mRNA of vascular endothelial growth factor (VEGF, 32.3±5.6 versus 13.1±3.7, P<0.05,) and angiopoietin‐2 (23.9±3.6 versus 13.7±3.1, P<0.05) in ischaemic myocardium was significantly greater in the BM‐MNC group than the saline group. The capillary density in ischaemic myocardium demonstrated a significant positive correlation with VEGF expression (r=0.61, P<0.001).ConclusionCatheter‐based direct intramyocardial injection of BM‐MNC enhanced angiogenesis more effectively than BM‐EPC or saline, possibly via a paracrine effect, with increased expression of VEGF that subsequently improved cardiac performance of ischaemic myocardium.
Identification of the Photorespiratory 2-Phosphoglycolate Phosphatase, PGLP1, in Arabidopsis
Authors: Schwarte Sandra , Bauwe Hermann 
Published: May 2007

AbstractThe chloroplastidal enzyme 2-phosphoglycolate phosphatase (PGLP), PGLP1, catalyzes the first reaction of the photorespiratory C2 cycle, a major pathway of plant primary metabolism. Thirteen potential PGLP genes are annotated in the Arabidopsis (Arabidopsis thaliana) genome; however, none of these genes has been functionally characterized, and the gene encoding the photorespiratory PGLP is not known. Here, we report on the identification of the PGLP1 gene in a higher plant and provide functional evidence for a second, nonphotorespiratory PGLP, PGLP2. Two candidate genes, At5g36700 (AtPGLP1) and At5g47760 (AtPGLP2), were selected by sequence similarity to known PGLPs from microorganisms. The two encoded proteins were overexpressed in Escherichia coli and both show PGLP activity. T-DNA knockout of one of these genes, At5g36700, results in very low leaf PGLP activity. The mutant is unviable in normal air but grows well in air enriched with 0.9% CO2. In contrast, deletion of At5g47760 does not result in a visible phenotype, and leaf PGLP activity is unaltered. Sequencing of genomic DNA from another PGLP-deficient mutant revealed a combined missense and missplicing point mutation in At5g36700. These combined data establish At5g36700 as the gene encoding the photorespiratory PGLP, PGLP1.