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Reliable Surrogate (reliable + surrogate)
Selected AbstractsA simulation approach to determine statistical significance of species turnover peaks in a species-rich tropical cloud forestDIVERSITY AND DISTRIBUTIONS, Issue 6 2007K. Bach ABSTRACT Use of ,-diversity indices in the study of spatial distribution of species diversity is hampered by the difficulty of applying significance tests. To overcome this problem we used a simulation approach in a study of species turnover of ferns, aroids, bromeliads, and melastomes along an elevational gradient from 1700 m to 3400 m in a species-rich tropical cloud forest of Bolivia. Three parameters of species turnover (number of upper/lower elevational species limits per elevational step, Wilson,Shmida similarity index between adjacent steps) were analysed. Significant species turnover limits were detected at 2000 (± 50) m and 3050 m, which roughly coincided with the elevational limits of the main vegetation types recognized in the study area. The taxon specificity of elevational distributions implies that no single plant group can be used as a reliable surrogate for overall plant diversity and that the response to future climate change will be taxon-specific, potentially leading to the formation of plant communities lacking modern analogues. Mean elevational range size of plant species was 490 m (± 369). Elevational range sizes of terrestrial species were shorter than those of epiphytes. We conclude that our simulation approach provides an alternative approach for assessing the statistical significance of levels of species turnover along ecological gradient without the limitations imposed by traditional statistical approaches. [source] Drug-eluting bead therapy in primary and metastatic disease of the liverHPB, Issue 7 2009Stewart Carter Abstract Background:, Drug-eluting bead transarterial chemoembolization (DEB-TACE) is a novel therapy for the treatment of hypervascuarized tumours. Through the intra-arterial delivery of microspheres, DEB-TACE allows for embolization as well as local release of chemotherapy in the treatment of hepatic malignancy, providing an alternative therapeutic option in unresectable tumours. Its role as an adjunct to surgical resection or radiofrequency ablation (RFA) is less clear. The purpose of this review is to summarize recent studies investigating DEB-TACE in order to better define safety, efficacy and outcomes associated with its use. Methods:, A systematic review of all published articles and trials identified nine clinical trials and 23 abstracts. These were reviewed for tumour histology, stage of treatment, delivery technique, outcome at follow-up, complications and mortality rates. Results:, Publications involved treatment of hepatocellular carcinoma (HCC), metastatic colorectal carcinoma (MCRC), metastatic neuroendocrine (MNE) disease and cholangiocarcinoma (CCA). Using Response Evaluation Criteria in Solid Tumours (RECIST) or European Association for the Study of the Liver (EASL) criteria, studies treating HCC reported complete response (CR) rates of 5% (5/101) at 1 month, 9% (8/91) at 4 months, 14% (19/138) at 6 months and 25% (2/8) at 10 months. Partial response (PR) was reported as 58% (76/131) at 1 month, 50% (67/119) at 4 months, 57% (62/108) at 6,7 months and 63% (5/8) at 10 months. Studies involving MCRC, CCA and MNE disease were less valuable in terms of response rate because there is a lack of comparative data. The most common procedure-associated complications included fever (46,72%), nausea and vomiting (42,47%), abdominal pain (44,80%) and liver abscess (2,3%). Rather than reporting individual symptoms, two studies reported rates of post-embolic syndrome (PES), consisting of fever, abdominal pain, and nausea and vomiting, at 82% (75/91). Six of eight studies reported length of hospital stay, which averaged 2.3 days per procedure. Mortality was reported as occurring in 10 of 456 (2%) procedures, or 10 of 214 (5%) patients. Conclusions:, Drug-eluting bead TACE is becoming more widely utilized in primary and liver-dominant metastatic disease of the liver. Outcomes of success must be expanded beyond response rates because these are not a reliable surrogate for progression-free survival or overall survival. Ongoing clinical trials will further clarify the optimal timing and strategy of this technology. [source] Real Options: Meeting the Georgetown ChallangeJOURNAL OF APPLIED CORPORATE FINANCE, Issue 2 2005Thomas E. Copeland In response to the demand for a single, generally accepted real options methodology, this article proposes a four-step process leading to a practical solution to most applications of real option analysis. The first step is familiar: calculate the standard net present value of the project assuming no managerial flexibility, which results in a value estimate (and a "branch" of a decision tree) for each year of the project's life. The second step estimates the volatility of the value of the project and produces a value tree designed to capture the main sources of uncertainty. Note that the authors focus on the uncertainty about overall project value, which is driven by uncertainty in revenue growth, operating margins, operating leverage, input costs, and technology. The key point here is that, in contrast to many real options approaches, none of these variables taken alone is assumed to be a reliable surrogate for the uncertainty of the project itself. For example, in assessing the option value of a proven oil reserve, the relevant measure of volatility is the volatility not of oil prices, but of the value of the operating entity,that is, the project value without leverage. The third step attempts to capture managerial flexibility using a decision "tree" that illustrates the decisions to be made, their possible outcomes, and their corresponding probabilities. The article illustrate various kinds of applications, including a phased investment in a chemical plant (which is treated as a compound option) and an investment in a peak-load power plant (a switching option with changing variance, which precludes the use of constant risk-neutral probabilities as in standard decision tree analysis). The fourth and final step uses a "no-arbitrage" approach to form a replicating portfolio with the same payouts as the real option. For most corporate investment projects, it is impossible to locate a "twin security" that trades in the market. In the absence of such a security, the conventional NPV of a project (again, without flexibility) is the best candidate for a perfectly correlated underlying asset because it represents management's best estimate of value based on the expected cash flows of the project. [source] Review article: renal function assessment in cirrhosis , difficulties and alternative measurementsALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 7 2007E. CHOLONGITAS Summary Background, Renal function in patients with cirrhosis is important prognostically, both before and following liver transplantation. Its prognostic impact is reflected by the inclusion of serum creatinine in the model for end-stage liver disease score, which is now used for recipient prioritization on liver transplantation waiting lists in the USA. Aim, To review the accuracy of the surrogate markers for the assessment of renal function, i.e. glomerular filtration rate, particularly in patients with cirrhosis. Method, We reviewed the available literature in PubMed regarding the markers for GFR evaluation and the factors which affect their accuracy in cirrhosis. Results, Although creatinine is widely available, it is an unreliable marker of glomerular filtration rate, particularly in patients with cirrhosis. Clearance of exogenous markers is considered the ,gold standard', but this methodology has many drawbacks, particularly poor applicability. Several mathematical formulae for estimated glomerular filtration rate are used to overcome some of these limitations: Cockcroft-Gault and Modification of Diet in Renal Disease formulae are the most frequently applied, but they are based on serum creatinine. Conclusions, Due to the inaccuracy of serum creatinine and its derived formulae in estimating glomerular filtration rate, alternative serum markers, such as cystatin C, and new formulae are desirable. These need formal evaluation in patients with cirrhosis so as to have a reliable surrogate of glomerular filtration rate, and to obviate many problems that are associated with using creatinine and estimated glomerular filtration rate. [source] | ||||||||||