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Data Aggregation (data + aggregation)
Selected AbstractsTrust management in wireless sensor networksEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 4 2010Theodore Zahariadis The range of applications of wireless sensor networks is so wide that it tends to invade our every day life. In the future, a sensor network will survey our health, our home, the roads we follow, the office or the industry we work in or even the aircrafts we use, in an attempt to enhance our safety. However, the wireless sensor networks themselves are prone to security attacks. The list of security attacks, although already very long, continues to augment impeding the expansion of these networks. The trust management schemes consist of a powerful tool for the detection of unexpected node behaviours (either faulty or malicious). Once misbehaving nodes are detected, their neighbours can use this information to avoid cooperating with them, either for data forwarding, data aggregation or any other cooperative function. A variety of trust models which follow different directions regarding the distribution of measurement functionality, the monitored behaviours and the way measurements are used to calculate/define the node's trustworthiness has been presented in the literature. In this paper, we survey trust models in an attempt to explore the interplay among the implementation requirements, the resource consumption and the achieved security. Our goal is to draw guidelines for the design of deployable trust model designs with respect to the available node and network capabilities and application peculiarities. Copyright © 2010 John Wiley & Sons, Ltd. [source] The impact of cross-sectional data aggregation on the measurement of vertical price transmission: An experiment with German food pricesAGRIBUSINESS : AN INTERNATIONAL JOURNAL, Issue 4 2006Stephan von Cramon-Taubadel The impact of cross-sectional aggregation over individual retail stores on the estimation and testing of vertical price transmission between the wholesale and retail levels is investigated using a unique data set of individual retail prices in Germany. Systematic differences between the results of estimations using aggregated data on the one hand, and disaggregated data on the other, are discussed theoretically and confirmed empirically. The results suggest that estimation with aggregated data can generate misleading conclusions about price transmission behavior at the level of the individual units (i.e., retail stores) that underlie these aggregates. [JEL classifications: C22, L11, D40] © 2006 Wiley Periodicals, Inc. Agribusiness 22: 505,522, 2006. [source] Standardizing Emergency Department,based Migraine Research: An Analysis of Commonly Used Clinical Trial Outcome MeasuresACADEMIC EMERGENCY MEDICINE, Issue 1 2010Benjamin W. Friedman MD Abstract Objectives:, Although many high-quality migraine clinical trials have been performed in the emergency department (ED) setting, almost as many different primary outcome measures have been used, making data aggregation and meta-analysis difficult. The authors assessed commonly used migraine trial outcomes in two ways. First, the authors examined the association of each commonly used outcome versus the following patient-centered variable: the research subject's wish, when asked 24 hours after investigational medication administration, to receive the same medication the next time they presented to an ED with migraine ("would take again"). This variable was chosen as the criterion standard because it provides a simple, dichotomous, clinically sensible outcome, which allows migraineurs to factor important intangibles of efficacy and adverse effects of treatment into an overall assessment of care. The second part of the analysis assessed how sensitive to true efficacy each outcome measure was by calculating sample size requirements based on results observed in previously conducted clinical trials. Methods:, This was a secondary analysis of data previously collected in four ED-based migraine randomized trials performed between 2003 and 2007. In each of these trials, subjects were asked 24 hours after administration of an investigational medication whether or not they would want to receive the same medication the next time they came to the ED with a migraine. Odds ratios (ORs) with 95% confidence intervals (CIs), adjusted for sex and medication received, were calculated as measures of association between the most commonly used outcome measures and "would take again." The sensitivity of each outcome measure to treatment efficacy was determined by calculating the sample size that would be required to detect a statistically significant result using estimates of that outcome obtained in two clinical trials. Results:, Data from 378 subjects were used for this analysis. Adjusted ORs for association of "would take again" and other commonly used primary headache outcomes are as follows: achieving a pain-free state by 2 hours, OR = 3.1 (95% CI = 1.8 to 5.4); sustained pain-free status, OR = 4.5 (95% CI = 1.9 to 11.0); and no need for rescue medication, OR = 3.7 (95% CI = 2.1 to 6.6). An improvement on a standardized 11-point pain scale of ,33% had an adjusted OR = 5.2 (95% CI = 2.2 to 12.4). The best performing alternate outcome, ,33% improvement, correctly classified 288 subjects and misclassified 77 subjects when compared to "would take again." At least 33% improvement and pain-free by 2 hours required the smallest sample sizes, while sustained pain-free and "would take again" required many more subjects. Conclusions:, "Would take again" was associated with all migraine outcome measures we examined. No individual outcome was more closely associated with "would take again" than any other. Even the best-performing alternate outcome misclassified more than 20% of subjects. However, sample sizes based on "would take again" tended to be larger than other outcome measures. On the basis of these findings and this outcome measure's inherent patient-centered focus, "would take again," included as a secondary outcome in all ED migraine trials, is proposed. ACADEMIC EMERGENCY MEDICINE 2010; 17:72,79 © 2010 by the Society for Academic Emergency Medicine [source] On testing predictions of species relative abundance from maximum entropy optimisationOIKOS, Issue 4 2010Stephen H. Roxburgh A randomisation test is described for assessing relative abundance predictions from the maximum entropy approach to biodiversity. The null model underlying the test randomly allocates observed abundances to species, but retains key aspects of the structure of the observed communities; site richness, species composition, and trait covariance. Three test statistics are used to explore different characteristics of the predictions. Two are based on pairwise comparisons between observed and predicted species abundances (RMSE, RMSESqrt). The third statistic is novel and is based on community-level abundance patterns, using an index calculated from the observed and predicted community entropies (EDiff). Validation of the test to quantify type I and type II error rates showed no evidence of bias or circularity, confirming the dependencies quantified by Roxburgh and Mokany (2007) and Shipley (2007) have been fully accounted for within the null model. Application of the test to the vineyard data of Shipley et al. (2006) and to an Australian grassland dataset indicated significant departures from the null model, suggesting the integration of species trait information within the maximum entropy framework can successfully predict species abundance patterns. The paper concludes with some general comments on the use of maximum entropy in ecology, including a discussion of the mathematics underlying the Maxent optimisation algorithm and its implementation, the role of absent species in generating biased predictions, and some comments on determining the most appropriate level of data aggregation for Maxent analysis. [source] Structured intervention utilizing state professional societies to foster quality improvement in practiceTHE JOURNAL OF CONTINUING EDUCATION IN THE HEALTH PROFESSIONS, Issue 3 2008Suzanne Lazorick MD Abstract Introduction: Despite the existence of guidelines for attention deficit hyperactivity disorder (ADHD), clinical practices vary substantially. Practitioners can apply quality improvement (QI) strategies to adapt office processes and clinical practice towards evidence-based care. We identified facilitators and barriers to participation in a professional society,led structured collaborative to learn QI methods and improve care. Methods: Ten chapters of the American Academy of Pediatrics participated in the effort. Support to chapter leaders included conference calls, listserv, technical support, and data aggregation. Support from the chapters to participating pediatricians included online continuing medical education modules, a workshop, chart reviews, and QI coaching. Qualitative data were obtained through interviews of 22 project leaders and reviews of project progress reports. Quantitative results were obtained from surveys of 186 physician participants. Outcomes included facilitators/barriers to program implementation, evidence for sustained chapter QI infrastructure, and participant assessment of improvements in care. Results: Facilitators included physician opinion leaders, a workshop, conference calls, QI support, and opportunities for shared learning. Barriers included lack of time, competing clinical priorities, challenges of using the online module, and underutilization of listservs. Seven chapters planned ongoing activities around attention deficit hyperactivity disorder (ADHD), eight had specific plans to use QI infrastructure for additional clinical topics, and three developed significant QI infrastructure. Physicians believed care improved. Discussion: As requirements grow for participation in QI for maintenance of certification, national and state-level professional societies are interested in and can develop infrastructure to support quality improvement. Coaching, tools, and support from the national organization and QI experts are helpful in facilitating efforts. [source] What influence do anticoagulants have on oral implant therapy?CLINICAL ORAL IMPLANTS RESEARCH, Issue 2009A systematic review Abstract Objectives: This systematic review aims to assess the risks (both thromboembolic and bleeding) of an oral anticoagulation therapy (OAT) patient undergoing implant therapy and to provide a management protocol to patients under OAT undergoing implant therapy. Material and methods: Medline, Cochrane Data Base of Systematic Reviews, the Cochrane Central Register of Controlled Trials and EMBASE (from 1980 to December 2008) were searched for English-language articles published between 1966 and 2008. This search was completed by a hand research accessing the references cited in all identified publications. Results: Nineteen studies were identified reporting outcomes after oral surgery procedures (mostly dental extractions in patients on OAT following different management protocols and haemostatic therapies). Five studies were randomized-controlled trials (RCTs), 11 were controlled clinical trials (CCTs) and three were prospective case series. The OAT management strategies as well as the protocols during and after surgery were different. This heterogeneity prevented any possible data aggregation and synthesis. The results from these studies are very homogeneous, reporting minor bleeding in very few patients, without a significant difference between the OAT patients who continue with the vitamin K antagonists vs. the patients who stopped this medication before surgery. These post-operative bleeding events were controlled only with local haemostatic measures: tranexamic acid mouthwashes, gelatine sponges and cellulose gauzes's application were effective. Post-operative bleeding did not correlate with the international normalised ratio (INR) status. In none of the studies was a thromboembolic event reported. Conclusions: OAT patients (INR 2,4) who do not discontinue the AC medication do not have a significantly higher risk of post-operative bleeding than non-OAT patients and they also do not have a higher risk of post-operative bleeding than OAT patients who discontinue the medication. In patients with OAT (INR 2,4) without discontinuation, topical haemostatic agents were effective in preventing post-operative bleeding. OAT discontinuation is not recommended for minor oral surgery, such as single tooth extraction or implant placement, provided that this does not involve autogenous bone grafts, extensive flaps or osteotomy preparations extending outside the bony envelope. Evidence does not support that dental implant placement in patients on OAT is contraindicated. [source] The income elasticity of meat: a meta-analysisAUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 4 2010Craig A. Gallet The demand for meat has been estimated by many studies utilizing various data and estimation methods. In this study, we perform a meta-analysis of the income elasticity of meat that involves regressing 3357 estimated income elasticities, collected from 393 studies, on variables that control for study characteristics. Across several meta-regression specifications, we find significant differences in income elasticities tied to the type of meat being studied, as well as a few functional forms, data aggregations, publication characteristics, and locations of demand. However, many study characteristics do not significantly influence reported income elasticities. Less concern should be given to such characteristics when choosing an income elasticity from the literature. [source] | |||||||||||||