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981.
We examine bias in Markov models of diseases, including both chronic and infectious diseases. We consider two common types of Markov disease models: ones where disease progression changes by severity of disease, and ones where progression of disease changes in time or by age. We find sufficient conditions for bias to exist in models with aggregated transition probabilities when compared to models with state/time dependent transition probabilities. We also find that when aggregating data to compute transition probabilities, bias increases with the degree of data aggregation. We illustrate by examining bias in Markov models of Hepatitis C, Alzheimer’s disease, and lung cancer using medical data and find that the bias is significant depending on the method used to aggregate the data. A key implication is that by not incorporating state/time dependent transition probabilities, studies that use Markov models of diseases may be significantly overestimating or underestimating disease progression. This could potentially result in incorrect recommendations from cost-effectiveness studies and incorrect disease burden forecasts. 相似文献
982.
Neuropsychiatric signs are critical in primary caregiving of Alzheimer patients and yet have been relatively ignored in murine models. In the present study, APPswe/PS1 bigenic mice had higher levels of irritability than non-transgenic controls as measured in the touch escape test. Moreover, APPswe/PS1 mice showed poorer nest building than controls and a higher duration of immobility in the forced swimming assay. These results are concordant with the hypothesis of increased apathy and depression-like behavior in an Alzheimer's disease model. In addition, APPswe/PS1 bigenic mice were deficient in retention of passive avoidance learning and left–right discrimination learning, concordant with previous findings in other Alzheimer-like models. 相似文献
983.
D. P. Sleeman J. Davenport S. J. More T. A. Clegg J. M. Griffin I. O’Boyle 《European Journal of Wildlife Research》2009,55(3):267-278
This study’s objective was to estimate the permeability of barriers to badger immigration during the Irish Four Area project.
These barriers were at the boundaries of removal areas, where there was proactive culling of badgers. Data from the last 3 years
of the study were used. Each length of barrier was allocated a space within the removal area. These were further sub-divided
into spaces of 0–2, 2–5 km and sometimes of more than 5 km from the edge of the removal area. It is assumed that all, or some,
of the badgers caught within these spaces came across the barriers. The barriers were one of the following: external buffers,
sea, rivers and political boundaries. The total lengths of the barriers in all areas were: external buffer 128.5 km; sea 70.9 km;
river 78.6 km; political 32.2 km. We assume three scenarios: (1) all badgers caught in the final 3 years were immigrants,
(2) 75% were immigrants or (3) 50% were immigrants. We test these scenarios using chi-square tests, applying internal buffers
of 1 km to counter movements of badgers across zones. Using this approach and multivariate analysis, we found that the permeability
of barrier types varied, with sea and external buffers being the most effective barriers. The combined capture data are further
examined by the sex ratio in each range, and then the sex ratio in total. Equal numbers of males and females were found, but
the source populations were probably predominantly female. If badger management options are to achieve maximum benefits, then
the field effectiveness of such barriers needs to be understood. 相似文献
984.
Synthetic waters imitating BOD5 test conditions have been studied to model the progress curves of cell growth, organic matter consumption and oxygen demand.
Glucose and glutamic acid were used as organic matter and Bacillus subtilis, Escherichia coli and Pseudomonas putida as microorganisms. The concentrations of all the products were measured simultaneously over time and were fitted to the Logistic
and Monod models. Following this, the goodness of fit was analysed. Discrimination between models allowed us to conclude that
the Logistic model has acceptable accuracy to describe the kinetic behaviour inside a BOD5 bottle, while the extra parameter in the Monod model would not be statistically justified. Thus, the logistic parameters
were determined under different conditions by non-linear regression and their biological meaning was interpreted. 相似文献
985.
986.
Leili Jia Jiyun Yu Jinliang Yang Hongbin Song Xuelin Liu Yong Wang Yuanyong Xu Chuanfu Zhang Yanwei Zhong Qiao Li 《International journal of biological sciences》2009,5(5):421-427
Hepatitis C virus (HCV) heterogeneity accounts for the failure of effective vaccine development and the lack of successful anti-viral therapy in some patients. Little is known about the immune response to HCV peptides and the region or race specific genotypes in China. The objective of this study was to characterize HCV antibody immune response to HCV peptides and HCV genotypes in different regions and races of China. A total of 363 serum samples were collected from HCV carriers in 6 regions in China. The immune response to HCV peptides was evaluated by ELISA. HCV genotypes were examined using nested RT-PCR. We found that the anti-HCV antibody neutralization rates were significantly different among the serum samples from different areas or from different races in the same area. For samples from Tibet and Sinkiang, the rates of neutralization by HCV peptides were only 3.2% and 30.8%, respectively. The genotypes of samples from Tibet and Sinkiang were apparently heterogeneic and included type I, II, III and multiple types (I/II/III, I/II, I/III, II/III). One specific sample with multiple-genotype (I/II/III) HCV infection was found to consist of type I, II, III, II/III and an unclassified genotype. These studies indicate that the anti-HCV antibody immune response to HCV peptides varied across regions and among races. The distribution of HCV genotypes among Tibetans in Tibet and Uighurs in Sinkiang was different from that in the inner areas of China. In addition, a “master” genotype, type II, was found to exist in HCV infection with multiple HCV genotypes. 相似文献
987.
Consider a set of baseline predictors X to predict a binaryoutcome D and let Y be a novel marker or predictor. This paperis concerned with evaluating the performance of the augmentedrisk model P(D = 1|Y,X) compared with the baseline model P(D= 1|X). The diagnostic likelihood ratio, DLRX(y), quantifiesthe change in risk obtained with knowledge of Y = y for a subjectwith baseline risk factors X. The notion is commonly used inclinical medicine to quantify the increment in risk predictiondue to Y. It is contrasted here with the notion of covariate-adjustedeffect of Y in the augmented risk model. We also propose methodsfor making inference about DLRX(y). Case–control studydesigns are accommodated. The methods provide a mechanism toinvestigate if the predictive information in Y varies with baselinecovariates. In addition, we show that when combined with a baselinerisk model and information about the population distributionof Y given X, covariate-specific predictiveness curves can beestimated. These curves are useful to an individual in decidingif ascertainment of Y is likely to be informative or not forhim. We illustrate with data from 2 studies: one is a studyof the performance of hearing screening tests for infants, andthe other concerns the value of serum creatinine in diagnosingrenal artery stenosis. 相似文献
988.
Oral administration of antibiotics to treat dental problems mostly yields slow actions due to slow onset and hepatic “first-pass.”
Again, commonly used dental paints are generally washed out by saliva within few hours of application. To overcome the challenges,
polymeric molds to be placed on an affected tooth (during carries and gum problems) were prepared and evaluated in vitro for sustained drug release for prolonged local action. Here, amoxicillin trihydrate and lidocaine hydrochloride were used
as model drugs. Dental molds were prepared using corn zein, carbopol 934 P, gum karaya powder, and poloxamer 407 by mixing
and solvent evaporation technique. Different physicochemical evaluation studies such as tooth adhesion test, surface pH, swelling
index, and drug-distribution pattern were carried out. Percentage swelling varied from 56% to 93%. Average tooth adhesion
strength and mean initial surface pH of the formulations were 50 g and 6.5, respectively. As assessed by scanning electron
microscopy, drug distribution was uniform throughout the matrix. Cumulative percentage release of lidocaine hydrochloride
and amoxicillin trihydrate in simulated saliva were 98% and 50%, respectively. In vitro drug-release studies revealed the sustained-release patterns of the drugs in simulated saliva at least for 24 h. The stability
study shows that the drugs were stable in the formulations following the conditions as per ICH guideline. The formulation
is a novel approach to deliver the drug(s) for a prolonged period for local action upon its application on an affected tooth. 相似文献
989.
T. Takken A. C. Blank E. H. Hulzebos M. van Brussel W. G. Groen P. J. Helders 《Netherlands heart journal》2009,17(9):339-344
Cardiopulmonary exercise testing (CPET) in paediatric cardiology differs in many aspects from the tests as performed in adult cardiology. Children's cardiovascular responses during exercise testing present different characteristics, particularly oxygen uptake, heart rate and blood pressure response, which are essential in interpreting haemodynamic data. Diseases that are associated with myocardial ischaemia are very rare in children. The main indications for CPET in children are evaluation of exercise capacity and the identification of exercise-induced arrhythmias. In this article we will review exercise equipment and test protocols for CPET in children with congenital heart disease. (Neth Heart J 2009;17:339–44.) 相似文献
990.
We tested the genetic and ecological differences between neighbouring urban and rural populations of common kestrels (Falco tinnuculus) in southern Bohemia. The aims were to (1) assess the genetic variability of the studied kestrel populations using microsatellite
markers, (2) check the genetic relatedness of individuals within the urbanization gradient, and (3) compare possible gradients
of body characteristics and reproductive parameters on the urbanization gradient. The mean expected allelic polymorphism did
not differ among the studied populations, which were not genetically separated (F
ST
= 0.0003, P = 0.781). Also, an individual assignment test did not show a separation of these populations. Urban kestrels that bred in
the city centre were indicatively more related than others, and no relationship was found in the rural kestrel population.
Kestrel females were heavier towards the city centre, but males did not show this relationship. Nest distance from the city
centre had no significant effect on any of the tested reproductive parameters. Our results do not support the notion of genetic
differentiation between rural and urban kestrels, but revealed trends in body characteristics and genetic relatedness along
the urbanization gradient. 相似文献