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Debate: Are surrogate end-point studies worth the effort?
Jonathan Valabhji, Robert S Elkeles
Trials , 2000, DOI: 10.1186/cvm-1-2-072
Abstract: Although cardiovascular disease is the commonest cause of death in Western countries, the large number of cardiovascular events result from a low absolute event rate in a large number of people. Prospective trials that assess the effect of an intervention on event rate therefore require large numbers of subjects to be followed for many years, at huge expense. This has led investigators to use surrogate endpoints. With the use of surrogate end-points, every participant can reach an end-point, which is usually a continuous rather than a categorical variable. As a result, sufficient power can be attained by studying much smaller numbers of subjects for shorter periods of time. There are, however, inherent problems with this approach. The validity of a surrogate end-point must be established. This in itself requires a prospective study, adequately powered, to demonstrate that the surrogate end-point is able to predict future cardiovascular events. Furthermore, for a surrogate end-point to be worthwhile, its ability to predict future cardiovascular events must exceed that of conventional risk factors.Surrogate end-points that have been used to assess the risk of cardiovascular events, and to which this commentary will be restricted, include the following: resting 12-lead electrocardiogram; coronary artery luminal diameters assessed by coronary angiography; arterial stiffness assessed directly, as change in luminal diameter during the cardiac cycle adjusted for lumen diameter and pulse pressure, or indirectly, as pulse wave velocity; brachial artery flow-mediated dilatation; carotid and femoral artery IMT; and coronary artery calcification detected by EBCT.One of the early surrogate end-points was the resting 12-lead electrocardiogram. In the Honolulu heart programme [1] both major and minor electrocardiogram abnormalities were predictive of subsequent coronary heart disease (CHD) events. Minnesota-coded ECG events were also used in the 10-year follow up of the Bedford su
Plagiarism: avoiding the slippery slope  [cached]
David Jonathan Castle
Andhra Pradesh Journal of Psychological Medicine , 2012,
Abstract:
A perfect correlate does not a surrogate make
Stuart G Baker, Barnett S Kramer
BMC Medical Research Methodology , 2003, DOI: 10.1186/1471-2288-3-16
Abstract: We use a graphical approach. The vertical axis is the unobserved true endpoint and the horizontal axis is the potential surrogate endpoint. Perfect correlation within each randomization group implies that, for each randomization group, potential surrogate and true endpoints are related by a straight line. In this scenario the investigator does not know the slopes or intercepts. We consider a plausible example where the slope of the line is higher for the experimental group than for the control group.In our example with unknown lines, a decrease in mean potential surrogate endpoints from control to experimental groups corresponds to an increase in mean true endpoint from control to experimental groups. Thus the potential surrogate endpoints give the wrong inference. Similar results hold for binary potential surrogate and true outcomes (although the notion of correlation does not apply). The potential surrogate endpointwould give the correct inference if either (i) the unknown lines for the two group coincided, which means that the distribution of true endpoint conditional on potential surrogate endpoint does not depend on treatment group, which is called the Prentice Criterion or (ii) if one could accurately predict the lines based on data from prior studies.Perfect correlation between potential surrogate and unobserved true outcomes within randomized groups does not guarantee correct inference based on a potential surrogate endpoint. Even in early phase trials, investigators should not base conclusions on potential surrogate endpoints in which the only validation is high correlation with the true endpoint within a group.A potential surrogate endpoint is an endpoint obtained sooner, at less cost, or less invasively than the true endpoint of interest. When using a potential surrogate endpoint, one would like to make the same inference as if one had observed a true endpoint (i.e. a health outcome). Fleming and DeMets [1] and the Biomarker Definitions Working Group [2]
Conversa??es sobre a "boa morte": o debate bioético acerca da eutanásia
Siqueira-Batista, Rodrigo;Schramm, Fermin Roland;
Cadernos de Saúde Pública , 2005, DOI: 10.1590/S0102-311X2005000100013
Abstract: despite extensive current debate on euthanasia, many open and apparently unsolvable issues persist, awaiting a better conceptual treatment. the area includes "prejudices and fundamentalisms" in relation to the theme, still viewed as taboo by a major share of society, specifically in the case of brazil, while semantic imprecision in the term and argumentative tensions surround the issue, focusing on the principles of sacredness of life, quality of life, and autonomy and the so-called "slippery slope" argument. the purpose of the current essay is thus to serve as a sphere of inquiry concerning euthanasia, moving from historical antecedents towards a better solution to the problem and the demarcation of necessary future perspectives for enhanced understanding of the issue.
Using patient management as a surrogate for patient health outcomes in diagnostic test evaluation
Lukas P Staub, Sarah J Lord, R Simes, Suzanne Dyer, Nehmat Houssami, Robert YM Chen, Les Irwig
BMC Medical Research Methodology , 2012, DOI: 10.1186/1471-2288-12-12
Abstract: We discuss the rationale for measuring patient management, describe the common study designs and provide guidance about how this evidence should be reported.Interpretation of patient management studies relies on the condition that patient management is a valid surrogate for downstream patient benefits. This condition presupposes two critical assumptions: the test improves diagnostic accuracy; and the measured changes in patient management improve patient health outcomes. The validity of this evidence depends on the certainty around these critical assumptions and the ability of the study design to minimise bias. Three common designs are test RCTs that measure patient management as a primary endpoint, diagnostic before-after studies that compare planned patient management before and after testing, and accuracy studies that are extended to report on the actual treatment or further tests received following a positive and negative test result.Patient management can be measured as a surrogate outcome for test evaluation if its limitations are recognised. The potential consequences of a positive and negative test result on patient management should be pre-specified and the potential patient benefits of these management changes clearly stated. Randomised comparisons will provide higher quality evidence about differences in patient management using the new test than observational studies. Regardless of the study design used, the critical assumption that patient management is a valid surrogate for downstream patient benefits or harms must be discussed in these studies.Before a new test is introduced in clinical practice, evidence is needed to demonstrate that its use will lead to improvements in patient health outcomes [1]. Studies reporting test accuracy may not be sufficient, and clinical trials of tests that follow patients over the whole pathway from testing to treatment outcomes, although ideal, are rarely feasible [2]. Therefore, studies investigating the consequences o
Outcomes intermedios Surrogate outcomes
Ignacio Neumann,Juan Carlos Claro G-A
Revista médica de Chile , 2012,
Abstract:
Condensation on Slippery Asymmetric Bumps  [PDF]
Kyoo-Chul Park,Philseok Kim,Neil He,Joanna Aizenberg
Physics , 2015,
Abstract: Bumps are omnipresent from human skin to the geological structures on planets, which offer distinct advantages in numerous phenomena including structural color, drag reduction, and extreme wettability. Although the topographical parameters of bumps such as radius of curvature of convex regions significantly influence various phenomena including anti-reflective structures and contact time of impacting droplets, the effect of the detailed bump topography on growth and transport of condensates have not been clearly understood. Inspired by the millimetric bumps of the Namib Desert beetle, here we report the identified role of radius of curvature and width of bumps with homogeneous surface wettability in growth rate, coalescence and transport of water droplets. Further rational design of asymmetric convex topography and synergetic combination with slippery coating simultaneously enable self-transport, leading to unseen five-fold higher growth rate and an order of magnitude faster shedding time of droplets compared to superhydrophobic surfaces. We envision that our fundamental understanding and innovative design of bumps can be applied to lead enhanced performance in various phase change applications including water harvesting.
Slippery or sticky ! Control of wrinkling patterns by selective adhesion  [PDF]
Hugues Vandeparre,Julien Léopoldès,Christophe Poulard,Sylvain Desprez,Gwennaelle Derue,Cyprien Gay,Pascal Damman
Physics , 2007,
Abstract: Wrinkling patterns at the metallized surface of thin polymer films are shown to be sensitive to the sticky or slippery character of the polymer/substrate interface (titanium coating, polystyrene film and coated silicon substrate). Selective prefered wrinkle orientation and amplitude are achieved. Existing theoretical models are expanded to specific boundary conditions (adhesive vs slippery) and rationalize these observations.
Investigation of the sliding friction behaviors of locust on slippery plates
LiXin Wang,Qiang Zhou,ShuYan Xu,HuLi Niu
Chinese Science Bulletin , 2009, DOI: 10.1007/s11434-009-0576-6
Abstract: The slippery trapping plate in swarm locust control is a method of realizing resource utilization of locust and avoiding pesticide residues in the entironment. Some slippery plates with different material composition or surface characteristic were investigated through the sliding tests of locust on slippery plates, and sliding rubbing behaviors of locusts on the plate were observed by means of CCD video monitoring system. Poor sliding character of silicate glass to locust was verified, which is in accordance with the adhesive effect generated by secretion of locust feet pads on the smooth surface. And also, PVC plastic plate presents a poor sliding character to locusts, because the soft surface of PVC can permit claws of locust feet to engender mechanical interlock on the surface. The zinc plate shows a considerable slippery ratio for locusts because of the appropriate surface characteristic and material property. Photoelectric stimulation for resting locust can promote the movement of locust. Accordingly, the contact form of locust feet and abdomen on slippery plates is changed and contact area is reduced severely, so the sliding effect of locust on slippery plates is strengthened effectively. These results supply a suitable theoretical foundation for manufacturing locust slippery trapping plates and trapping units, and indicate the important role of photoelectric stimulating factors in biotribology.
Investigation of slippery behaviour of lubricating fluid coated smooth hydrophilic surfaces  [PDF]
Reeta Pant,Pritam Kumar Roy,Arun Kumar Nagarajan,Krishnacharya Khare
Physics , 2015,
Abstract: In the recent years many research groups have studied slippery properties on lubricating fluid infused rough surfaces using hydrophobic substrates. These surfaces show excellent slippery behaviour for water and other liquids. Here we demonstrate a simple method to fabricate stable slippery surfaces based on silicone oil coated hydrophilic samples. At room temperature, as prepared samples exhibit non-slippery behaviour due to sinking of water drops inside silicone oil layer because of inherently hydrophilic silicon substrate. Subsequent annealing at higher temperatures provides covalent bonding of silicone molecules at silicon surface making the surface hydrophobic which was confirmed by lubricant wash tests. So the silicone oil coated annealed samples show excellent water repellency, very low contact angle hysteresis and very good slippery behavior. But these surfaces show poor oil stability against drops flow due to cloaking of the oil around water drops which can be prevented by using drops of larger volume or continuous flow of water.
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