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Methods for dealing with tied event times in the Cox proportional hazards model are well developed. Also, the partial likelihood provides a natural way to handle covariates that change over time. However, ties between event times and the times that discrete time-varying covariates change have not been systematically studied in the literature. In this article, we discuss the default behavior of current software and propose some simple methods for dealing with such ties. A simulation study shows that the default behavior of current software can lead to biased estimates of the coefficient of a binary time-varying covariate and that two proposed methods (Random Jitter and Equally Weighted) reduce estimation bias. The proposed methods can be easily implemented with existing software. The methods are illustrated on the well-known Stanford heart transplant data and data from a study on intimate partner violence and smoking. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study represents a survey performed among staff who, according to the Ionising Radiation (Medical Exposures) Regulations of 2000 (IRMER), are responsible for justifying radiological examinations in the UK. The aim of the survey is to map the current situation regarding knowledge of risks from X-ray exposures and the criteria used for their justification. An anonymous electronic questionnaire was emailed to 219 radiologists and radiographers of five National Health Service hospitals. The questions were designed to investigate the way the sample group defines/assesses risk and benefit when justifying medical exposures, and to test their knowledge on radiation doses, risk communication, and on relevant national legislation. The majority of the respondents are aware of the relevant legislation/guidelines. Patient's medical condition, age and sex, and alternative techniques using less or no ionising radiation are the main criteria used for justification. However, when estimating the effective dose of various examinations in chest radiograph equivalents, the majority of the responses were incorrect. Although there is good knowledge of legislation around justification of medical exposures, there seems to be a lack of knowledge on radiation doses and risks among IRMER practitioners. [ABSTRACT FROM PUBLISHER]

Nest predation is an important practical challenge for the conservation of egg-laying reptiles, with the potential to reduce hatchling recruitment and slow the recovery of threatened populations. Accurately forecasting where and when predation will occur has the potential to optimize predation management. Survival analysis, a set of statistical techniques recently popularized in studies of avian nest success, provides a unique approach for modelling variation in egg mortality risk throughout development. We used Cox proportional hazards regression to model the survival of sea turtle eggs from predation by the small Asian mongoose Herpestes javanicus, a widely introduced and destructive sea turtle nest predator in the Caribbean. We evaluated the ability of models to predict egg survival using 7 years of nest predation data for critically endangered hawksbill sea turtles Eretmochelys imbracata in Barbados. Daily predation risk was the highest for freshly laid nests, decreasing rapidly with nest age but increasing again near the end of development. Predation risk was the highest in and near patches of beach vegetation, increased over the nesting season and increased with nest density on the open beach but not in vegetation. Survival models calibrated using data from 2004 to 2005 showed excellent discrimination and ≥84% accuracy when predicting the fate of nests from previous years. Our study provides the first quantification of the daily variation in predation risk for incubating turtle eggs, revealing a narrow time window early in development during which the application of predation reduction measures is likely to have the greatest impact on nest survival. More generally, we demonstrate the utility of survival analysis for generating fine-scale predictions of spatiotemporal variation in turtle egg mortality, providing a flexible tool for the conservation of sea turtles and other egg-laying reptiles. [ABSTRACT FROM AUTHOR]

The article examines the origin and characteristics of hares in Barbados. Based on a study by C. H. W. Feilden, it is reported that European hares, Lepus europaeus, were shipped to Barbados in 1842 in which they were bred in captivity and escaped after a heavy rain destroyed their enclosure. It notes that by the 1940s, hares became common in the country and that they were abundant in open and grassy areas. Surveys on the hares of Barbados also reveal that part of their diet was a sugar cane trash and stalks left in the fields or cart roads by sugar cane workers. It also mentions that apart from sugar cane trash, hares also eat crops, slips of plants, and the bark of young trees.

Title. Creating case scenarios or vignettes using factorial study design methods.Aim. This paper is a report of a study conducted to develop clinical case vignettes using an adaptation of an incomplete factorial study design methodology.Background. In health care, vignettes or cases scenarios are core to problem-based learning, common in practice guideline development processes, and increasingly being used in patient or care-giver studies of chronic or life-threatening illnesses. A large number of behavioural, psycho-social and clinical factors can be relevant in such decision problems. Unbiased methods for choosing what factors to include are needed, when it is not possible to include all relevant combinations of factors in the vignettes.Method. The factors to be considered, number of levels or categories for each factor, and desired number of scenarios were decided in advance. An algorithm was used first to create the full factorial data set, and then a random subset of combinations was generated, according to predefined criteria, based on maximizing determinants. The subset of combinations was incorporated into written vignettes. The study was conducted in 2004-2005.Findings. Application of the method yielded diverse and balanced scenarios that covered the full range of factors to be considered for a project to elicit health providers' processes in diet counselling for dyslipidemia.Conclusion. The approach is flexible, decreases possible researcher bias in the creation of vignettes, and can improve statistical power in survey research. This novel application of study design methodology merits consideration when vignettes are being developed to elicit opinions or decisions in studies of complex health issues. [ABSTRACT FROM AUTHOR]

The marine turtle fishery of Grenada was assessed using interviews with marine turtle fishermen and by examination of turtle catch data from a major landing site. An estimated 782 turtles, mainly Endangered green turtles Chelonia mydas and Critically Endangered hawksbill turtles Eretmochelys imbricata, were caught around Grenada and its sister island Carriacou each year between 1996 and 2001 during an annual 8-month open season, with only a small percentage being officially recorded at a landing site. Turtles were primarily caught with nets and spearguns, with more green turtles caught by net fishermen and more hawks-bill turtles by spear fishermen. Catch per unit effort data suggested that relative abundance had declined since the previous estimate was made in 1969. Few adult green or loggerhead turtles Caretta caretta were caught, indicating the relative scarcity of this size class of these two species around Grenada. Adult-sized hawksbill turtles were caught regularly, with larger adults being caught in the non-breeding months of the open season than in the breeding months. A higher percentage of adult hawksbill turtles present during the breeding season are likely to be animals that nest in Grenada, and their smaller size may result from historically heavy fishing pressure. The larger sized adults caught during the non-breeding season are likely to be animals that forage around Grenada but breed elsewhere in the Caribbean where they are protected. [ABSTRACT FROM AUTHOR]

This paper describes the clinical presentation of 360 patients suffering from "dyspepsia" at the time of their initial visit to two hospitals in Yorkshire. Disease categories studied were cholecystitis, duodenal ulcer, gastric ulcer, gastric cancer, and "functional" dyspepsia, with at least 50 patients in each category. The findings of this series are contrasted with "textbook" descriptions of these conditions. Some contrasts are quite surprising-for example, most of the 360 patients claimed that their pain was not aggravated by food. It is suggested that one reason for diagnostic error in this area of medicine is that clinicians have a faulty mental "database" of information with regard to the presentation of the various diseases concerned. [ABSTRACT FROM PUBLISHER]

This paper reports a comparison in Airedale District General Hospital between computer-aided diagnosis of dyspepsia and endoscopy in a prospective unselected series of 165 patients. Patients were interviewed immediately before endoscopy and the findings analysed by a small desk-top computer-aided system. Each 'new' patient was compared by the computer with a group of 360 similar patients from Leeds (25 miles away). Overall, 83% of the positive lesions found at endoscopy were correctly predicted by the computer, including all but three of the 22 cases of gastric cancer. It is suggested (1) that there is little loss of accuracy in transferring the computer-aided system from one locality to another; and (2) that a computer-aided analysis of the patient interview may be of value in selecting 'high-risk' patients for intensive investigation. [ABSTRACT FROM PUBLISHER]

A simple, rapid colorimetric method for the estimation of phosphoglucose isomerase activity, using the determination of fructose by the method of Roe, Epstein, and Goldstein (1949), is described. An arbitrary fructose standard is advocated and normal values for human serum and cerebrospinal fluid are presented. [ABSTRACT FROM PUBLISHER]