bluuebunny/crossref_metadata_2025 huggingface dataset:
A systematic review of the impact of volume of surgery and specialization on patient outcome
Authors: Chowdhury M M , Dagash H , Pierro A
Published: January 2007

Background and methods

Volume of surgery and specialization may affect patient outcome. Articles examining the effects of one or more of three variables (hospital volume of surgery, surgeon volume and specialization) on outcome (measured by length of hospital stay, mortality and complication rate) were analysed. Reviews, opinion articles and observational studies were excluded. The methodological quality of each study was assessed, a correlation between the variables analysed and the outcome accepted if it was significant.

Results

The search identified 55 391 articles published between 1957 and 2002; 1075 were relevant to the study, of which 163 (9 904 850 patients) fulfilled the entry criteria. These 163 examined 42 different surgical procedures, spanning 13 surgical specialities. None were randomized and 40 investigated more than one variable. Hospital volume was reported in 127 studies; high-volume hospitals had significantly better outcomes in 74·2 per cent of studies, but this effect was limited in prospective studies (40 per cent). Surgeon volume was reported in 58 studies; high-volume surgeons had significantly better outcomes in 74 per cent of studies. Specialization was reported in 22 studies; specialist surgeons had significantly better outcomes than general surgeons in 91 per cent of studies. The benefit of high surgeon volume and specialization varied in magnitude between specialities.

Conclusion

High surgeon volume and specialization are associated with improved patient outcome, while high hospital volume is of limited benefit.
Minimally invasive pancreatic necrosectomy
Authors: Windsor J A
Published: January 2007

Increasing in popularity
Systematic review of enhanced recovery programmes in colonic surgery (Br J Surg 2003; 93: 800–809)
Authors: Walter C , Collin J
Published: January 2007

The Editors welcome topical correspondence from readers relating to articles published in the Journal. Responses should be sent electronically via the BJS website (www.bjs.co.uk). All letters will be reviewed and, if approved, appear on the website.A selection of these will be edited and publishe in the Journal. Letters must be no more than 250 words in length.
Colorectal cancer with synchronous liver metastases
Authors: Adam R
Published: January 2007

Management in a state of flux
Electrochemiluminescent Cells Based on Zeolite‐Encapsulated Host–Guest Systems: Encapsulated Ruthenium Tris‐bipyridyl
Authors: Álvaro Mercedes , Cabeza Jose F. , Fabuel David , Corma Avelino , García Hermenegildo
Published: February 2007

An electrochemiluminescent cell has been developed that has an active layer consisting of ruthenium tris‐bipyridyl encapsulated inside zeolite Y supercages. Operation of the cell requires the addition of polyethylene glycol as the solid electrolyte. The cell, which exhibits electrical conductivity behavior typical of a semiconductor, has an optimum operating voltage of 3 V. Ion exchange of sodium by cesium and vapor deposition of calcium metal inside the zeolite pores enhance the electrochemiluminescent efficiency of the cell by a factor of 4.
Stille–Heck Coupling Sequences Applied in a Versatile New Access to Steroid Skeletons
Authors: Sünnemann Hans Wolf , Hofmeister Anja , Magull Jörg , de Meijere Armin
Published: January 2007

A variety of enantiomerically pure steroidal compounds was synthesized utilizing a sequence of Stille and Heck cross‐coupling reactions and subsequent thermal 6π‐electrocyclizations. Highly chemoselective Stille couplings on the triflate moiety of several 2‐bromocyclohex‐1‐enyl triflates with cis‐ and trans‐fused bicyclo[4.3.0]nonenylstannanes furnished the corresponding tricyclic bromobutadienes in good to excellent yields (70–97 %). These were subjected to Heck reactions with tert‐butyl acrylate to provide pentasubstituted tricyclic 1,3,5‐hexatrienes. A significant increase in efficiency could be achieved by applying a novel protocol with a precatalyst on the basis of the palladacycle prepared from Pd(OAc)2 and P(o‐Tol)3 with added triarylphosphines as co‐ligands (73–90 % yield). Upon heating to 205–215 °C in decalin or to 140 °C in toluene (for certain cases), these hexatrienes yielded (78–90 %) various unsaturated steroid analogues as single diastereomers. A particular oxohexatriene, obtained after deprotection of an adjacent carbonyl group, underwent 6π‐electrocyclization at the unusually low temperature of 140 °C to yield (75 %) an interesting 7‐carboxyl‐substituted steroidal dienone. Attempts to remove the remaining protecting groups from some of the other new steroidal compounds under acidic conditions furnished a novel 3‐oxo‐7‐carboxyl steroid analogue and a 3‐hydroxy‐substituted steroidal diene. A novel estradiol derivative could be obtained in 69 % yield from the synthesized steroidal dienone. Deprotection furnished the corresponding unprotected 7‐carboxylestradiol in 81 % yield.
Novel Structural Motifs Consisting of Chiral Thiazolines: Synthesis, Molecular Recognition, and Anticancer Activity
Authors: Han Fu She , Osajima Hiroyuki , Cheung Mui , Tokuyama Hidetoshi , Fukuyama Tohru
Published: February 2007

The facile synthesis of linear and cyclic chiral oligo(4‐α/β‐methyl)thiazolines is described. Linear oligothiazolines have been efficiently synthesized by the iterative formation of thiazoline rings and two‐directional block condensation. The construction of 24‐ to 36‐membered cyclic oligothiazolines was achieved through the head‐to‐tail cyclo‐oligomerization of doubly deprotected linear fragments. Studies of the interactions of both the linear and cyclic oligomers with chiral compounds revealed that cyclic oligomers displayed a strong binding affinity towards mandelic acid, whereas linear oligomers showed a poor affinity. Linear oligomers have been proven to inhibit the cell growth of the cancer cell lines HPAC, PC‐3, and HCT‐116. Studies of the structure–activity relationships showed that the IC50 values are clearly dependent on both the length and the terminal functionalities of the linear oligomers. Longer derivatives showed more potent activity (e.g., hexi‐ and octithiazolines exhibit IC50<1 μM) against all three cancer cell lines. In sharp contrast, cyclic oligomers were inactive to all three cell lines.
Measuring the effect of field strength on noise amplification factor
Authors: Kelley Douglas A.C.
Published: February 2007

As shown previously, parallel imaging techniques should benefit significantly from higher field strengths due to a reduction in noise amplification (g) factor. The intent of this study was to measure directly the role of field strength in this reduction, comparing the measured g factors for two commercial eight‐channel head array coils of similar mechanical design at 3T and 7T using low and high permittivity phantoms. The results indicated that the lower g factors result primarily from the RF standing wave pattern and the greater spatial complexity of the coil sensitivities in high permittivity materials at high frequency, although the physical design of the array elements plays an important role in controlling the growth of noise amplification. A simplified method of g factor measurement for an array coil is also presented. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 31B: 51–59, 2007
Purkinje cell compartmentation as revealed by Zebrin II expression in the cerebellar cortex of pigeons (Columba livia)
Authors: Pakan Janelle M.P. , Iwaniuk Andrew N. , Wylie Douglas R.W. , Hawkes Richard , Marzban Hassan
Published: February 2007

Purkinje cells in the cerebellum express the antigen zebrin II (aldolase C) in many vertebrates. In mammals, zebrin is expressed in a parasagittal fashion, with alternating immunopositive and immunonegative stripes. Whether a similar pattern is expressed in birds is unknown. Here we present the first investigation into zebrin II expression in a bird: the adult pigeon (Columba livia). Western blotting of pigeon cerebellar homogenates reveals a single polypeptide with an apparent molecular weight of 36 kDa that is indistinguishable from zebrin II in the mouse. Zebrin II expression in the pigeon cerebellum is prominent in Purkinje cells, including their dendrites, somata, axons, and axon terminals. Parasagittal stripes were apparent with bands of Purkinje cells that strongly expressed zebrin II (+ve) alternating with bands that expressed zebrin II weakly or not at all (−ve). The stripes were most prominent in folium IXcd, where there were seven +ve/−ve stripes, bilaterally. In folia VI–IXab, several thin stripes were observed spanning the mediolateral extent of the folia, including three pairs of +ve/−ve stripes that extended across the lateral surface of the cerebellum. In folium VI the zebrin II expression in Purkinje cells was stronger overall, resulting in less apparent stripes. In folia II–V, four distinct +ve/−ve stripes were apparent. Finally, in folia I (lingula) and X (nodulus) all Purkinje cells strongly expressed zebrin II. These data are compared with studies of zebrin II expression in other species, as well as physiological and neuroanatomical studies that address the parasagittal organization of the pigeon cerebellum. J. Comp. Neurol. 501:619–630, 2007. © 2007 Wiley‐Liss, Inc.
Cadherin expression in the developing mouse olfactory system
Authors: Akins Michael R. , Benson Deanna L. , Greer Charles A.
Published: February 2007

Although odor receptors have been implicated in establishing the topography of olfactory sensory neurons (OSNs) in the olfactory bulb (OB), it is likely other molecules are also involved. The cadherins (CDHs) are a large family of cell adhesion molecules that mediate cell:cell interactions elsewhere in the central nervous system. However, their distribution and role in the olfactory system have remained largely unexplored. We previously demonstrated that intracellular binding partners of cadherins, the catenins, have unique spatiotemporal patterns of expression in the developing olfactory system. To further our understanding of cadherin function within the developing olfactory system, we now report on the localization of 11 classical cadherins—CDH1, 2, 3, 4, 5, 6, 8, 10, 11, 13, and 15. We demonstrate the expression of all but CDH5 and CDH15 in neuronal and/or glial cells in primary olfactory structures. CDH1 and CDH2 are expressed by OSNs; CDH2 expression closely parallels that seen for γ‐catenin in OSN axons. CDH3 and CDH11 are expressed by olfactory ensheathing glia, which surround OSN axons in the outer OB. CDH2, CDH4, and CDH6 are expressed within neuropil. CDH2, CDH4, CDH6, CDH8, CDH10, CDH11, and CDH13 are expressed by projection neurons within the main and accessory OBs. We conclude that cadherin proteins in the developing olfactory system are positioned to underlie the formation of the odorant map and local circuits within the OB. J. Comp. Neurol. 501:483–497, 2007. © 2007 Wiley‐Liss, Inc.
A Conformational Analysis Method for Understanding the Energy Landscapes of Clusters
Authors: Cheng Longjiu , Cai Wensheng , Shao Xueguang
Published: February 2007

A newly developed unbiased structural optimization method, named dynamic lattice searching (DLS), is proposed as an approach for conformational analysis of atomic/molecular clusters and used in understanding the energy landscape of large clusters. The structures of clusters are described in terms of the number of basic tetrahedron (BT) units they contain. We found that the hit numbers of different structural motifs in DLS runs is proportional to the number of BTs. A parameter Tmax is defined to limit the maximal number of atoms moved in a structural transition. Results show that Tmax is a key parameter for modulating the efficiency of the DLS method and has a great influence on the hit number of different motifs in DLS runs. Finally, the effect of potential range on the conformational distribution of the (Morse)98 cluster is also discussed with different potential‐range parameters.
Social rank and attachment in people with a bipolar disorder
Authors: Gilbert P. , McEwan K. , Hay J. , Irons C. , Cheung M.
Published: January 2007

This paper explores the relationship between personal evaluations of attachment and personal evaluations of social rank, in relationship to mood variation in bipolar disorder. Forty patients with diagnosed bipolar affective disorder, who were regarded as ‘relatively stable’ by their psychiatrist, were given a set of self‐report questionnaires, measuring attachment style, social comparison, submissive behaviour and various aspects of mood. Mood variation within this group was highly linked to variation in social rank evaluations. In particular, elevated mood was associated with feeling superior, while depression was associated with feeling inferior. Attachment also varied with mood but appeared to be less related to mood in this group. This study suggests that variation in social rank evaluations may be significantly associated with mood variation in patients with a bipolar disorder. Copyright © 2007 John Wiley & Sons, Ltd.
The subjective experience of paranoia: Comparing the experiences of patients with psychosis and individuals with no psychiatric history
Authors: Campbell Michelle L. C. , Morrison Anthony P.
Published: January 2007

Over the last decade, significant theoretical developments in psychological approaches to paranoia have taken place. Despite this, no published research has examined the subjective experience of paranoia. The present study aimed to do this. 12 people took part; six of whom had received a diagnosis of a schizophrenia spectrum disorder and six had never received a psychiatric diagnosis but had experienced paranoid thoughts. Participants were interviewed and the data were then transcribed and analysed using interpretative phenomenological analysis (IPA). Four superordinate themes were identified: (1) the phenomena; (2) beliefs about paranoia; (3) factors that influence paranoia; and (4) the consequences of paranoia. Within each theme, similarities and differences between the groups were highlighted. All participants believed that negative life experiences had influenced their paranoid ideas and all experienced anxiety. However, the most striking difference concerned the issue of control; the patient group felt controlled by their ideas whereas the non‐patients did not. The theoretical and clinical implications of the findings are discussed. Copyright © 2007 John Wiley & Sons, Ltd.
Early maladaptive schemas in children: Stability and differences between a community and a clinic referred sample
Authors: Stallard Paul
Published: January 2007

This study explores whether the Early Maladaptive Schemas (EMS) proposed by Young (1994) are stable in children and whether EMS in community and clinical populations differ. The Schema Questionnaire for Children, (SQC), was completed twice by 77 children (9 out of 10 years) six months apart. The SQC completed by a community group (n = 46) attending a local school and those treated (n = 53) at a specialist child mental health clinic were compared. Significant correlations over time were found for 8 out of 12 of the EMS assessed. Significant differences between the community and referred group were found for 10 out of 12 EMS. These results are consistent with the key theoretical assumptions underlying schema therapy. Further research is required with larger samples of children to substantiate these findings. Copyright © 2007 John Wiley & Sons, Ltd.
Attributional biases in subclinical depression: A schema‐based account
Authors: Morris Steven J.
Published: January 2007

Non‐depressed individuals exhibit a self‐serving attributional bias, taking more credit for success than for failure. Clinically and subclinically depressed people are less self‐serving, often to the point of making similar attributions (explanations) for successes and failures. The present studies evaluated a schematic account of these distinct attributional biases. Subclinically depressed and non‐depressed participants completed measures of attributional bias (the relative strength of ability attributions for success versus failure), schema‐based optimism (the relative expectedness of success versus failure) and self‐schemas of competence. Two studies evaluated a hypothesis derived from the schematic account: the greater the perceived competence and optimism, the more self‐serving the attributional bias. As predicted, (a) attributional bias scores covaried with optimism and competence scores in both magnitude and valence (or direction), (b) depressed‐non‐depressed differences in attributional biases paralleled differences in competence and optimism and (c) when attributional bias scores were adjusted for the effects of optimism or competence, depressed–non‐depressed differences in attributional biases were eliminated. The schematic account raises questions about the common assumptions that attributional patterns are traits, and that they play a central role in the aetiology and treatment of depression. Copyright © 2007 John Wiley & Sons, Ltd.
Clinical psychology trainees' research productivity and publications: An initial survey and contributing factors
Authors: Cooper Myra , Turpin Graham
Published: January 2007

Clinical psychology research productivity is an issue of great professional concern. The current paper explores the rate and nature of trainee publication of research projects in peer‐reviewed journals, together with reasons likely to be relevant to its success and failure. Twenty‐one out of 28 courses responded to a survey composed of closed and open‐ended questions. Data were analysed using inferential statistics and content analysis. Twenty‐four percent of trainees in any one cohort during the period 1999–2004 successfully wrote up their research for publication. Most publications were in psychology journals with modest but respectable impact factors. The most important theme thought to be related to success was supervisor factors, followed by trainee factors, general course factors, study characteristics and the demands of a new job following qualification. Recommendations to enhance publication success are made within the context of a broader discussion of the importance of facilitating the development of the new generation of clinical psychology researchers. Copyright © 2007 John Wiley & Sons, Ltd.
Identifying mechanisms of change in psychotherapy: Mediators of treatment outcome
Authors: Johansson Paul , Høglend Per
Published: January 2007

We know that psychotherapy works, but the processes and mechanisms underlying therapeutic change are still largely unknown. The study of mediators and moderators of change in psychotherapy is one way to improve our understanding of mechanisms operating in psychotherapy. Consensus is slowly building on how to define both mediators and moderators of change, while there is still a controversy on strategic issues, e.g., criteria for demonstrating causality. The rationales for mediator research are discussed, as well as some of the major obstacles inherent in this research area. Finally, we present some strategic considerations for future research. Copyright © 2007 John Wiley & Sons, Ltd.
Basic and complex emotions in depression and anxiety
Authors: Power M. J. , Tarsia M.
Published: January 2007

The current study was designed to assess the emotion states that occur across the clinical disorders of depression, anxiety and mixed anxiety depression. The emotion states were assessed using the Basic Emotions Scale, which includes a set of simple and complex emotions rationally derived from the basic emotions of sadness, anger, fear, disgust and happiness. The profiles of emotion states across the clinical disorders and across a matched healthy control group supported an analysis in which emotions related to sadness and disgust were elevated in the depressed and mixed disorders, whereas increased levels of anger and fear, and decreased levels of happiness did not distinguish between clinical groups but were found in all disorders in comparison to healthy controls. Further factor analyses gave support for the proposed basic emotions model and did not support alternative models such as the Positive Affect‐Negative Affect model. The findings demonstrate how a theoretically based emotion analysis can provide a useful foundation from which to explore the emotional disorders. Copyright © 2007 John Wiley & Sons, Ltd.
Estimation of the cost of asbestos abatement in public buildings in the state of California: An application of the bootstrap
Authors: Azen Stanley P. , Niland Joyce , Hayward Steven B. , Liu Kai‐Shen , Redinger Charles , Porter Preston
Published: February 2007

In response to California Assembly Bill No. 2070 (1986), an Asbestos Assessment Task Force was created to analyze the magnitude of the asbestos problem in public buildings in the State of California. A survey of 207 city‐owned and county‐owned buildings was carried out to determine the presence and condition of asbestos‐containing material. In addition, a ranking and priority system was developed to rank buildings according to the degree of asbestos hazard, and to estimate the costs of abatement and/or management according to this system. This information was then extrapolated to the universe of city/county buildings using bootstrapping procedures. It was estimated that the average cost for recommended asbestos abatement was $194 million (range $146–254 million). The average cost for total removal of all asbestos increased to $379 million (range $312–470 million).
Nonlinear regression models for correlated count data
Authors: Burnett R. T. , Shedden J. , Krewski D.
Published: February 2007

In this article, nonlinear regression models for correlated count data are examined. Correlation within clusters is modelled by a multivariate Gaussian mixing process on the log‐expectation scale. The regression parameters and the variance‐covariance parameters of the mixing process are estimated using quasi‐likelihood methods. An example involving temporal trends in hospital admissions for respiratory disease is used to illustrate the methods proposed.
A simple protocol for radiation dosimetry based on the order statistics from a poisson process
Authors: Fox David R.
Published: February 2007

In this paper problems associated with the sampling and estimation of the background gamma radiation dose‐rate are considered. The work described herein has been motivated by the large sampling effort of background gamma radiation undertaken in Western Australia by ALCOA of Australia coupled with the absence of any definitive sampling methodology. Certain best estimators are proposed and results given which permit the construction of [optimal] sampling protocols for radiological investigations.
Box‐cox transformation in the analysis of combined effects of mixtures of chemicals
Authors: Razzaghi Mehdi , Kodell Ralph L.
Published: February 2007

A new general approach to modelling the joint action of two non‐interactive toxicants is considered. It is shown that the proposed method provides a more refined characterization of a mixture of two chemicals. The method is based on using the Box‐Cox power transformation to derive the most suitable function of concentration to be used in a linear response function obtained from a linearizing transformation. The concepts of concentration and response additivity as two extreme cases of additive joint action are discussed and used to demonstrate the ideas of an “envelope of additivity”. Two examples are used to provide further illustration of the proposed approach.
A class of new probability distributions for modelling environmental evolution with periodic behaviour
Authors: Dimitrov B. , Khalil Z.
Published: February 2007

A new class of probability distributions is introduced. This class accentuates the periodic behaviour of environmental conditions in time and the random occurrence of some events on each period. A constructive approach is used following the logic of the appearance of random events in the evolution of real‐world systems. Some physical and probabilistic properties of the new distributions are discussed. Elementary statistical data models are considered and two types of estimations of the attributes of these distributions are offered. Numerical and graphical illustrations with simulated and observed data are used to motivate our suggestions.
Earthquake risk and insurance
Authors: Brillinger David R.
Published: February 2007

Our concern is with protection against natural catastrophes through financial insurance. Development of appropriate premium rates requires consideration of a wide variety of variables entering into the occurrence of the disaster, and a broad range of scientific and statistical investigations results. Topics discussed include: premium computation, distribution of large earthquakes in time, ground motion at sites, attenuation of energy with distance, damage description and actual practice in various countries. Statistical considerations that arise include: description, stochastic modelling, conditioning, spatial processes, (marked) point processes, uncertainty estimation and robust/resistant procedures. Study of the insurance problem is scientifically enlightening because it requires one to focus on the whole context of the problem; geology, seismology, earthquake engineering, and damage.
A flexible model for ground ozone concentration
Authors: Graf‐Jaccottet Monique
Published: February 2007

The statistical analysis of the concentration of air pollutants in the atmosphere is generally applied to a time series of average concentrations. Statistical difficulties arise from the non stationarity of the series, the nonnormality of the measured concentration, the lack of independence and the important influence of external factors. A new model is proposed for the time series consisting of daily averages of ground level ozone. The annual trend is modelled by a function of the length of day, the nonnormality is taken into account by a Box‐Cox transformation and the errors are supposed to be autoregressive of order 1. This method is applied to the analysis of NABEL (Nationales Beobachtungsnetz für Luftfremdstoffe) data (two years data from two locations), Switzerland.
Comparison of two medians using a two‐sample lognormal model in environmental contexts
Authors: Stoline Michael R.
Published: February 2007

A test procedure is derived for comparing medians in a lognormal two‐sample context where some data may be left‐censored owing to non‐detects. This procedure is an extension of the method introduced by Harris (1991). It is assumed that two independent samples of sizesn1andn2are available from two lognormal populations LN(μ1,σ1) and LN(μ2,σ2). The EM algorithm is used to obtain maximum likelihood estimates of the parameters in four cases:H1(μ1= μ2,σ1= σ2),H2(μ1≠ μ2,σ1= σ2),H3(μ1= μ2,σ1≠ σ2), andH4(μ1≠ μ2,σ1≠ σ2). A protocol is described for testing the equality of the two medians (H0: μ1= μ2versusHr: μ1≠ μ2). Two procedures are recommended for this test, depending on whether the population skewness parameters are equal: (H0: σ1= σ2) or not (Hr: σ1≠ σ2). Asymptotic chi‐square tests are used in the recommended protocol. Similarities and differences between these lognormal methods and their two‐sample normal symmetric counterparts are discussed with particular reference to the role of the assumption σ1= σ2in both contexts. A detailed case study example of the method is provided using data contained in Millard and Deverel (1988). Comparisons are made between the lognormal methodology introduced here and the non‐parametric methods used by Milard and Deverel (1988) in the analysis of these data.
Environmental monitoring, assessment and prediction of change
Authors: El‐Shaarawi A. H.
Published: February 2007

Estimating the present status, detecting and estimating trends, identifying problem areas, and testing for compliance with standards are some common goals of environmental monitoring programmes. Issues of concern when setting these programmes are what to measure, how and when to make these measurements, and how to interpret the data. The role of statistics in addressing these issues is discussed and illustrated using three examples. The first is the upstream/downstream Niagara River monitoring program which is used to: (1) estimate the loads of contaminants to the river and from the river to Lake Ontario; (2) compare the concentrations of various contaminants with water quality standards. The monitoring programme for the Fraser River provides the second example. The Fraser River has, in contrast to the Niagara River, a complicated hydrological cycle which needs to be considered when interpreting water quality changes. The third is the before and after time series experiments for environmental impact assessment. In these examples, parametric and non‐parametric methods are used to model seasonality and trends. Techniques for dealing with censored data are also discussed.
Matching sampling designs and significance tests in environmental studies
Authors: Evans J. C. , Coote B. G.
Published: February 2007

Traditional ANOVA models are often successfully employed in environmental fields. However, there is a need to carefully examine the basic design, the assumptions and the form of the analysis so that valid tests of significance and standard errors are used. Examples will show that wrong conclusions can be drawn if this is not done. Environmental studies usually deal with mixed models that contain some factors that are fixed (i.e. particular levels or effects are of interest) and others that are random (i.e. the levels of these factors are sampled from a larger population). The type of replication, and consequent choice of error, applied to testing any fixed effect depend on the underlying assumptions made. Examples illustrate that correct matching of designs, tests and standard erors will allow these traditional methods to be applied, using mixed‐models software, to a wide range of studies where standard textbook replication cannot be used.
Trend analysis: Time series and point process problems
Authors: Brillinger David R.
Published: February 2007

The concern is with trend analysis. The data may be time series or point process. Parametric, semi‐parametric and non‐parametric models and procedures are discussed. The problems and techniques are illustrated with examples taken from hydrology and seismology. There is review as well as some new analyses and proposals.
A discrete time logistic regression model for analyzing censored survival data
Authors: Maul A.
Published: February 2007

Consideration is given to survival data analysis by modelling the hazard as a discrete function of time. This is done for each individual who is examined independently from the other individuals of the sample observed. Assuming time has been divided into intervals of the same length, the hazard associated with any specific time interval is taken to be of the form of a logistic function including a number of time‐dependent covariates which serve to characterize the individual under consideration. Asymptotic maximum likelihood results are given for the estimation of both the regression coefficients in the hazard function and the survivor function corresponding to a given profile, i.e. the successive values of the different covariates. The likelihood ratio statistic for testing the effects of the various covariates in order to compare several survival curves with respect to longevity is also derived. The process of model fitting is illustrated by two examples referring to clinical trails on leukaemia and advanced lung cancer patients, respectively.
Data‐based mechanistic modelling and the rainfall‐flow non‐linearity
Authors: Young Peter C. , Beven Keith J.
Published: February 2007

Although rainfall‐flow processes have received much attention in the hydrological literature, the nature of the non‐linear processes involved in the relationship between rainfall and river flow still remains rather unclear. This paper outlines the first author's data‐based mechanistic (DBM) approach to model structure identification and parameter estimation for linear and non‐linear dynamic systems and uses it to explore afresh the non‐linear relationship between measured rainfall and flow in two typical catchments. Exploiting the power of recursive estimation, state dependent non‐linearities are identified objectively from the time series data and used as the basis for the estimation of non‐linear transfer function models of the rainfall—flow dynamics. These objectively identified models not only explain the data in a parametrically efficient manner but also reveal the possible parallel nature of the underlying physical processes within the catchments. The DBM modelling approach provides a useful tool for the further investigation of rainfall‐flow processes, as well as other linear and non‐linear environmental systems. Moreover, because DBM modelling uses recursive estimation, it provides a powerful vehicle for the design of real‐time, self‐adaptive environmental management systems. Finally, the paper points out how DBM models can often be interpreted directly in terms of dynamic conservation equations (mass, energy or momentum) associated with environmental flow processes and stresses the importance of parallel processes in this connection.
Survival analyses of radiated animals incorporating competing risks and covariates
Authors: Gupta Ramesh C. , Albanese Richard A.
Published: February 2007

The United States Air Force has been interested in studying the effect of different types of radiation encountered by its personnel in space. A study was, therefore, conducted at the USAF School of Aerospace Medicine, Brooks Air Force, Texas with rhesus monkeys as experimental subjects. These subjects were exposed to different types of radiation such as: (1) electromagnetic radiation; (2) electrons; (3) protons; and (4) nuclei of elements of higher numbers with different amount of radiation. These subjects were followed over a period of 338 months. In this paper an interesting problem related to health and radiation has been addressed. The effects of radiation, taking into account the cause of death (cancer or heart disease) along with the covariates such as sex, age, type of exposure, dose, are examined. A general log‐linear hazard model approach is studied. The model estimates the cause specific hazard rates, assuming piecewise exponential distribution, and exhibits the survival function for each of the covariate groups and the probability of death due to each cause. A data set called ‘Delayed Bio‐Effects Colony’, of radiated animals, is analysed and some conclusions are drawn. Overall the study has brought out the effect of high and low doses of radiation on both the male and female groups. The procedure presented in the paper distinguishes between time varying hazards. Thus the methodology may be useful for other survival related environmental problems, be this with regard to animal or human survival. Thus, the paper could contribute to its more widespread use.
Empirical bayes estimators for spatially correlated incidence rates
Authors: Devine Owen J. , Louis Thomas A. , Halloran M. Elizabeth
Published: February 2007

Assessments of the potential health impacts of contaminants and other environmental risk factors are often based on comparisons of disease rates among collections of spatially aligned areas. These comparisons are valid only if the observed rates adequately reflect the true underlying area‐specific risk. In areas with small populations, observed incidence values can be highly unstable and true risk differences among areas can be masked by spurious fluctuations in the observed rates. We examine the use of Bayes and empirical Bayes methods for stabilizing incidence rates observed in geographically aligned areas. While these methods improve stability, both the Bayes and empirical Bayes approaches produce a histogram of the estimates that is too narrow when compared to the true distribution of risk. Constrained empirical Bayes estimators have been developed that provide improved estimation of the variance of the true rates. We use simulations to compare the performance of Bayes, empirical Bayes, and constrained empirical Bayes approaches for estimating incidence rates in a variety of multivariate Gaussian scenarios with differing levels of spatial dependence. The mean squared error of estimation associated with the simulated observed rates was, on average, five times greater than that of the Bayes and empirical Bayes estimates. The sample variance of the standard Bayes and empirical Bayes estimates was consistently smaller than the variance of the simulated rates. The constrained estimators produced collections of rate estimates that dramatically improved estimation of the true dispersion of risk. In addition, the mean square error of the constrained empirical Bayes estimates was only slightly greater than that of the unconstrained rate estimates. We illustrate the use of empirical and constrained empirical Bayes estimators in an analysis of lung cancer mortality rates in Ohio.
Parameter and quantile estimation for the generalized extreme‐value distribution
Authors: Castillo Enrique , Hadi Ali S.
Published: February 2007

The generalized extreme‐value distribution (GEVD) was introduced by Jenkinson (1955). It is now widely used to model extremes of natural and environmental data. The GEVD has three parameters: a location parameter (−∞ < Λ < ∞), a scale parameter (α > 0) and a shape parameter (−∞ < k < ∞). The traditional methods of estimation (e.g., the maximum likelihood and the moments‐based methods) have problems either because the range of the distribution depends on the parameters, or because the mean and higher moments do not exist when k ≤ − 1. The currently favoured estimators are those obtained by the method of probability‐weighted moments (PWM). The PWM estimators are good for cases where −1/2 < k < 1/2. Outside this range of k, the PWM estimates may not exist and if they do exist they cannot be recommended because their performance worsens as k increases. In this paper, we propose a method for estimating the parameters and quantiles of the GEVD. The estimators are well‐defined for all possible combinations of parameter and sample values. They are also easy to compute as they are based on equations which involve only one variable (rather than three). A simulation study is implemented to evaluate the performance of the proposed method and to compare it with the PWM. The simulation results seem to indicate that the proposed method is comparable to the PWM for −1/2 < k < 1/2 but outside this range it gives a better performance. Two real‐life environmental data sets are used to illustrate the methodology.
Optimal sampling designs for dependent spatial units
Authors: Benedetti Roberto , Palma Daniela
Published: February 2007

A geographical domain is partitioned into a set, with cardinalityN, of areal units (i.e. census tracts), each of them having an attribute variablez.Observations are often to be recorded for a subsetSof areal units whose cardinality isn.Under the hypothesis of dependence of the underlying data generating processZ, the following questions are considered: which is the best linear unbiased estimator (BLUE) of the mean of the processZ, and which is the subsetSthat minimizes the variance of this estimator? A weighted average estimator is used and the performances of some combinatorial optimization algorithms are tested to solve this problem. The simulated annealing algorithm is shown to be a suitable solution even when dealing with large data sets. Moreover, numerical comparisons are made between sampling designs obtained by using simulated annealing and the classical simple random and systematic sampling criteria.
Factors regulating residual aluminium concentrations in treated waters
Authors: Driscoll Charles T. , Letterman Raymond D.
Published: February 2007

Elevated concentrations of residual aluminium (Al) is an important issue for water treatment facilities. Concerns associated with high concentrations of residual aluminium include increased turbidity in drinking water, reduced effectiveness of disinfection, decreased carrying capacity of the water distribution system as well as potential effects on human health. The objectives of this study were to review the literature on mechanisms for controlling residual aluminium concentrations and to conduct a field study to evaluate the forms of residual aluminium in three water treatment plants. Both the literature review and results of the field study suggest that elevated concentrations of residual aluminium appear to occur largely in either of two forms; particulate aluminium or dissolved (monomeric) aluminium. To decrease concentrations of residual aluminium which largely occur as monomeric aluminium, it is necessary to maintain the pH of treated water near the pH of minimum Al(OH)3 solubility (6.5–7.0), remembering that this value varies with temperature. Elevated concentrations of residual aluminium associated with particulate aluminium may be due to influent suspensions with a high aluminium content or relatively large amounts of aluminium coagulant per amount of particulate matter in raw water. The results of this study suggest that filtered water turbidity should be less than 0.1 NTU to minimize particulate aluminium concentrations that contribute to residual aluminium.
Statistical evaluation of selected air pollutants in Athens, Greece
Authors: Kambezidis H. D. , Tulleken R. , Amanatidis G. T. , Paliatsos A. G. , Asimakopoulos D. N.
Published: February 2007

A statistical evaluation of the air pollution situation in Athens for the year 1982 is presented. This analysis refers to NO2, NO, O3 and SO2 concentration levels measured at the National Observatory of Athens (NOA) with a fully automatic monitoring station. The seasonal, weekly and daily variations of the above pollutants are in agreement with the corresponding activities in the city which are responsible for these emissions. Auto‐ and cross‐correlation techniques are applied to the pollutants for January and July. It is found that all pollutants exhibit a well defined oscillatory behaviour because of their diurnal peaks in both months, except for NO2 in January whose auto‐correlation function shows no regular shape. For the same reason the January NO‐NO2 cross‐correlation function behaves in the same way; the pairs NO‐O3 and NO2‐O3 exhibit a clear oscillatory pattern. The spectral estimate method is also employed to the above pollutants for the two months in question. The energy content of O3, for instance, in July shows to be concentrated around a frequency corresponding to a periodicity of 24 hours.
Extension of spatial information, bayesian kriging and updating of prior variogram parameters
Authors: Cui Haiyan , Stein Alfred , Myers Don E.
Published: February 2007

Variograms are used to describe the spatial variability of environmental variables. In this study, the parameters that characterize the variogram are obtained from a variogram in a different but comparably polluted area. A procedure is presented for improving the variogram modelling when data become available from the area of interest. Interpolation is carried out by means of a Bayesian form of kriging, where prior distributions of the variogram parameters are used. This procedure differs from current procedures, since commonly applied least squares estimation for the variogram is avoided. The study is illustrated with data from a cadmium pollution in the Netherlands, where this form of extrapolation was compared with ordinary kriging. When sufficient data are available (more than 140), ordinary kriging gave the most precise predictions. When the number of data was small (i.e. less than 60), predictions obtained with Bayesian kriging were more precise as compared to those obtained with ordinary kriging. This leads to a considerable reduction of costs, without loss of information.
Case‐control designs for the detection of spatial clusters of diseases
Authors: Biggeri Annibale , Marchi Marco
Published: February 2007

To detect spatial clusters of rare diseases, an extension of the method proposed by Besag and Newell to the context of case‐control sampling is presented. For each case location a circle containing at leastkother disease cases is drawn. For each circle, the probability of type I error, under the null hypothesis of no clustering, is computed with the Poisson formula with parameter given by the product of the case‐control ratio times the numbercout ofNcontrols classified within the circle. In the paper a hierarchical Bayesian formulation of the problem is used to cope with the variability in the numbercof sampled controls. The observed number of cases is assumed to follow the Poisson‐binomial distribution with hyperparameterpmodelled as a beta (c+ 1,N‐c+ 1) random variate. A case‐control study on lung cancer in the River Serchio Valley 1987–90 (Tuscany, Italy) exemplifies the method. Statistically significant clusters of cases were found in the vicinity of a copper foundry.
Effect of atmospheric stability on concentration fluctuations and wake retention times for dispersion in the vicinity of an isolated building
Authors: Higson H. L. , Griffiths R. F. , Jones C. D. , Biltoft C.
Published: February 2007

This study is concerned with the effect of changes in atmospheric stability on concentration fluctuations near an isolated building. Field experiments were conducted to measure concentration fluctuations at several locations close to a model building, for continuous point sources upwind of the building. Experiments were conducted in flat terrain using a 2 m cube as the model. Concentrations were measured at a frequency of 200 Hz using a detector system with a response time of 1/50 second. Meteorological conditions varied from stable to unstable. Analysis of the time series of concentration produced by these experiments has shown that there are several periods when the gas behaves as if it were switched off at the source (due to shifts in the wind direction). Comparisons were made in such cases of the time taken for the source gas to evacuate the wake recirculation region. It was found that this period was several times longer in stable meteorological conditions than in unstable conditions. This finding has important implications in relation to hazard assessment near buildings.
Fixed‐point values of contaminant cloud dilution
Authors: Heagy W. K. , Sullivan P. J.
Published: February 2007

The contaminant concentration values that are experienced by a fixed observer are represented by an expected‐mass‐fraction function. It is shown that the α‐β prescription of moments enable the expected‐mass‐fraction to be approximated. The release of a puff of contaminant in the neutral atmospheric boundary layer is used as an illustrative example.
A contaminant‐dilution heuristic model
Authors: Labropulu F. , Sullivan P. J. , Ye H.
Published: February 2007

The sheet‐strand texture of a contaminant concentration field in turbulent flows is the basis of a simple model of the dilution process in contaminant clouds and plumes. The model is used to explain qualitative observations on kurtosis, skewness and probability density functions near the source in continuous line and point source plumes in grid turbulence.
Penalized regression in action: Estimating pollution roses from daily averages
Authors: Eilers Paul H. C.
Published: February 2007

A pollution rose consists of selective averages of concentrations of an air pollutant for all sectors of the wind rose. Generally the sectors are 10 or 20 degrees wide and one‐hour averages of concentrations and wind directions are used. Complications arise when daily averages of concentrations have to be used. The number of data is much smaller and the variability of the wind direction over 24 hours is large. In this paper, a linear regression model is presented and applied to a real set of data. The standard solution of the regression problem is shown to give useless results; this is a consequence of the ill‐conditioning (multicollinearity) of the data. Large improvements are achieved with ridge regression and other forms of penalized least squares estimation. Cross‐validation is used for obtaining good values of the penalty parameter automatically.