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Practical Constraints (practical + constraint)
Selected AbstractsEffects of Practical Constraints on Item Selection Rules at the Early Stages of Computerized Adaptive TestingJOURNAL OF EDUCATIONAL MEASUREMENT, Issue 2 2004Shu-Ying Chen The purpose of this study was to compare the effects of four item selection rules,(1) Fisher information (F), (2) Fisher information with a posterior distribution (FP), (3) Kullback-Leibler information with a posterior distribution (KP), and (4) completely randomized item selection (RN),with respect to the precision of trait estimation and the extent of item usage at the early stages of computerized adaptive testing. The comparison of the four item selection rules was carried out under three conditions: (1) using only the item information function as the item selection criterion; (2) using both the item information function and content balancing; and (3) using the item information function, content balancing, and item exposure control. When test length was less than 10 items, FP and KP tended to outperform F at extreme trait levels in Condition 1. However, in more realistic settings, it could not be concluded that FP and KP outperformed F, especially when item exposure control was imposed. When test length was greater than 10 items, the three nonrandom item selection procedures performed similarly no matter what the condition was, while F had slightly higher item usage. [source] Obstacles to Bottom-Up Implementation of Marine Ecosystem ManagementCONSERVATION BIOLOGY, Issue 5 2008KIRSTEN E. EVANS manejo de ecosistemas; manejo marino basado en ecosistemas; participación de partes interesadas; planificación de la conservación Abstract:,Ecosystem management (EM) offers a means to address multiple threats to marine resources. Despite recognition of the importance of stakeholder involvement, most efforts to implement EM in marine systems are the product of top-down regulatory control. We describe a rare, stakeholder-driven attempt to implement EM from the bottom up in San Juan County, Washington (U.S.A.). A citizens advisory group led a 2-year, highly participatory effort to develop an ecosystem-based management plan, guided by a preexisting conservation-planning framework. A key innovation was to incorporate social dimensions by designating both sociocultural and biodiversity targets in the planning process. Multiple obstacles hindered implementation of EM in this setting. Despite using a surrogate scheme, the information-related transaction costs of planning were substantial: information deficits prevented assessment of some biodiversity targets and insufficient resources combined with information deficits prevented scientific assessment of the sociocultural targets. Substantial uncertainty, practical constraints to stakeholder involvement, and the existence of multiple, potentially conflicting, objectives increased negotiation-related costs. Although information deficits and uncertainty, coupled with underinvestment in the transaction costs of planning, could reduce the long-term effectiveness of the plan itself, the social capital and momentum developed through the planning process could yield unforeseeable future gains in protection of marine resources. The obstacles we identified here will require early and sustained attention in efforts to implement ecosystem management in other grassroots settings. Resumen:,El manejo de ecosistemas es un medio para abordar múltiples amenazas a los recursos marinos. No obstante el reconocimiento de la importancia de la participación de las partes interesadas, la mayoría de los esfuerzos para implementar el manejo de ecosistemas en sistemas marinos son producto del control normativo de arriba hacia abajo. Describimos un intento raro, conducido por las partes interesadas, por implementar el manejo del ecosistema de abajo hacia arriba en el Condado San Juan, Washington (E.U.A.). Un grupo consultivo de ciudadanos dirigió un esfuerzo altamente participativo para desarrollar un plan de manejo basado en el ecosistema, guiados por un marco de planificación de la conservación preexistente. Una innovación clave fue la incorporación de dimensiones sociales al incluir objetivos tanto socioculturales como de biodiversidad en el proceso de planificación. Múltiples obstáculos dificultaron la implementación del manejo del ecosistema en este escenario. No obstante que se utilizó un plan sustituto, los costos de transacción de la planificación relacionados con la información fueron mayores de lo que el grupo pudo superar: los déficits de información impidieron la evaluación de algunos objetivos de biodiversidad y la insuficiencia de recursos combinada con los déficits de información impidieron la evaluación científica de los objetivos socioculturales. Los costos relacionados con la negociación incrementaron por la incertidumbre, por limitaciones prácticas en la participación de partes interesadas y la existencia de objetivos múltiples, potencialmente conflictivos. Aunque los déficits de información y la incertidumbre, aunados con la baja inversión en los costos de transacción de la planificación, pudieran reducir la efectividad a largo plazo del plan mismo, el capital social y el ímpetu desarrollados durante el proceso de planificación podrían producir ganancias futuras imprevisibles para la protección de recursos marinos. Los obstáculos que identificamos aquí requerirán de atención temprana y sostenida en los esfuerzos para implementar el manejo de ecosistemas en otros escenarios de base popular. [source] Landings, logbooks and observer surveys: improving the protocols for sampling commercial fisheriesFISH AND FISHERIES, Issue 2 2007A J R Cotter Abstract The sampling of commercial marine fisheries for management purposes often displays a key weakness in the form of poor documentation of the scientific basis of sampling and estimation, the assumptions made, and the practical constraints. This paper reviews systematically the theoretical and practical options that can remedy this situation and recommends that decisions be archived in regularly updated ,Sampling Approach and Modifications' (SAM) documents. Defining the target population, the observable population (usually a subset of the target), and the assumed links between them is important, along with the distinction between design- and model-based sampling approaches. Fleet-targeted and stock-targeted sampling strategies are contrasted, the latter being much harder to implement. Sampling protocols aimed at estimating quantities of fish landed and discarded, length,frequency distributions, length-related variables such as age, weight and maturity, and ratio variables such as catch per unit of effort and the proportions of discards are discussed, together with the raising of estimates to fleet and/or stock levels. The ideas are summarized in the specific contexts of landings sampling, logbook schemes and sea-going observer surveys. SAMs are commended for enhancing the scientific value of fishery sampling, and for encouraging methodological discussions among users and producers of the data. [source] Transgenic and knock-out mouse pups: the growing need for behavioral analysisGENES, BRAIN AND BEHAVIOR, Issue 3 2002I. Branchi Few laboratories working with transgenic and knock-out mice analyze the neurobehavioral consequences of genetic manipulation in early ontogeny. However, the study of behavioral endpoints during the early postnatal period in genetically modified mice is important not only to assess possible developmental abnormalities, but also to better understand and disentangle the effects of genetic manipulations in adulthood. We propose that the assessment of neurobehavioral development represents an appropriate strategy to identify possible compensatory and/or unexpected effects. Nowadays, a large number of experimental protocols that take into account the practical constraints imposed by the peculiar physiological and behavioral responses of an immature subject are available to assess the neurobehavioral profile of developing mice. While this knowledge should be applied to the field of transgenic and knock-out mice in general, it should be recommended, in particular, for the study of mouse models of neurodevelopmental disorders. [source] Limits on the detectability of the CMB B-mode polarization imposed by foregroundsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2005M. Tucci ABSTRACT We investigate which practical constraints are imposed by foregrounds on the detection of the B-mode polarization generated by gravitational waves, in the case of experiments of the type currently being planned. As the B-mode signal is probably dominated by foregrounds at all frequencies, the detection of the cosmological component depends drastically on our ability to remove foregrounds. We provide an analytical expression with which to estimate the level of the residual polarization for Galactic foregrounds, according to the method employed for their subtraction. We interpret this result in terms of the lower limit of the tensor-to-scalar ratio r that allows us to disentangle the cosmological B-mode polarization from the foreground contribution. Polarized emission from extragalactic radio sources and gravitational lensing is also taken into account. As a first approach, we consider the ideal limit of an instrumental noise-free experiment: for full-sky coverage and a resolution of 1°, we obtain a limit of r, 10,4. This value can be improved by high-resolution experiments and, in principle, there is no clear fundamental limit on the detectability of the polarization of gravitational waves. Our analysis is also applied to planned or hypothetical future polarization experiments, taking into account expected noise levels. [source] New approaches for solving the block-to-train assignment problemNETWORKS: AN INTERNATIONAL JOURNAL, Issue 1 2008Krishna C. Jha Abstract Railroad planning involves solving two optimization problems: (i) the blocking problem, which determines what blocks to make and how to route traffic over these blocks; and (ii) the train schedule design problem, which determines train origins, destinations, and routes. Once the blocking plan and train schedule have been obtained, the next step is to determine which trains should carry which blocks. This problem, known as the block-to-train assignment problem, is considered in this paper. We provide two formulations for this problem: an arc-based formulation and a path-based formulation. The latter is generally smaller than the former, and it can better handle practical constraints. We also propose exact and heuristic algorithms based on the path-based formulation. Our exact algorithm solves an integer programming formulation with CPLEX using both a priori generation and dynamic generation of paths. Our heuristic algorithms include a Lagrangian relaxation-based method as well as a greedy construction method. We present computational results of our algorithms using the data provided by a major US railroad. We show that we can obtain an optimal solution of the block-to-train assignment problem within a few minutes of computational time, and can obtain heuristic solutions with 1,2% deviations from the optimal solutions within a few seconds. © 2007 Wiley Periodicals, Inc. NETWORKS, 2008 [source] Diagnosis of vocal cord dysfunction in asthma with high resolution dynamic volume computerized tomography of the larynxRESPIROLOGY, Issue 8 2009Peter W. HOLMES ABSTRACT Background and objective: Vocal cord dysfunction (VCD) often masquerades as asthma and reports have suggested that up to 30% of patients with asthma may have coexistent VCD. Diagnosis of VCD is difficult, in part because it involves laryngoscopy which has practical constraints, and there is need for rapid non-invasive diagnosis. High speed 320-slice volume CT demonstrates laryngeal function during inspiration and expiration and may be useful in suspected VCD. Methods: Endoscopy and high resolution 320-slice dynamic volume CT were used to examine and compare laryngeal anatomy and movement in a case of subglottic stenosis and in a patient with confirmed VCD. Nine asthmatics with ongoing symptoms and suspected VCD also underwent 320-slice dynamic volume CT. Tracheal and laryngeal anatomy and movement were evaluated and luminal areas were measured. Reductions in vocal cord luminal area >40%, lasting for >70% duration of inspiration/expiration, were judged to be consistent with VCD. Results: Studies of subglottic tracheal stenosis validated anatomical similarities between endoscopy and CT images. Endoscopy and 320-slice volume CT also provided comparable dynamic images in a patient with confirmed VCD. A further nine patients with a history of severe asthma and suspected VCD were studied using CT. Four patients had evidence of VCD and the median reduction of luminal area during expiration was 78.2% (range 48.2,92.5%) compared with 10.4% (range 4.7,30%) in the five patients without VCD. Patients with VCD had no distinguishing clinical characteristics. Conclusions: Dynamic volume CT provided explicit images of the larynx, distinguished function of the vocal cords during the respiratory cycle and could identify putative VCD. The technique will potentially provide a simple, non-invasive investigation to identify laryngeal dysfunction, permitting improved management of asthma. [source] Watching the birdie watching you: eyewitness memory for actions using CCTV recordings of actual crimesAPPLIED COGNITIVE PSYCHOLOGY, Issue 4 2001Penny S. Woolnough In this paper we describe a method of assessing eyewitness performance for actual crimes that could prove a valuable addition to more traditional experimental and field-based approaches to the study of eyewitnessing. We present the findings of the first reported attempt to assess the accuracy of information contained in police statements given by eyewitnesses to actual criminal episodes using CCTV as a means of verification. Employing the criterion of using only those items that could be verified against CCTV recordings (largely action details), both victims and bystanders from eight incidents of assault were found to be highly accurate in their accounts (96% accurate). These results are discussed in terms of what they might indicate about the relationship between arousal and eyewitness performance and how they compare with laboratory and other field-based approaches to the study of eyewitness memory. In addition, we consider some of the methodological, technological and practical constraints associated with this novel approach and its possible future applications to the study of everyday memory as well as memory for unusual events. Copyright © 2001 John Wiley & Sons, Ltd. [source] ,O sibling, where art thou?'- a review of avian sibling recognition with respect to the mammalian literatureBIOLOGICAL REVIEWS, Issue 1 2004Shinichi Nakagawa ABSTRACT Avian literature on sibling recognition is rare compared to that developed by mammalian researchers. We compare avian and mammalian research on sibling recognition to identify why avian work is rare, how approaches differ and what avian and mammalian researchers can learn from each other. Three factors: (1) biological differences between birds and mammals, (2) conceptual biases and (3) practical constraints, appear to influence our current understanding. Avian research focuses on colonial species because sibling recognition is considered adaptive where,mixing potential'of dependent young is high; research on a wide range of species, breeding systems and ecological conditions is now needed. Studies of acoustic recognition cues dominate avian literature; other types of cues (e.g. visual, olfactory) deserve further attention. The effect of gender on avian sibling recognition has yet to be investigated; mammalian work shows that gender can have important influences. Most importantly, many researchers assume that birds recognise siblings through,direct familiarisation'(commonly known as associative learning or familiarity); future experiments should also incorporate tests for,indirect familiarisation'(commonly known as phenotype matching). If direct familiarisation proves crucial, avian research should investigate how periods of separation influence sibling discrimination. Mammalian researchers typically interpret sibling recognition in broad functional terms (nepotism, optimal outbreeding); some avian researchers more successfully identify specific and testable adaptive explanations, with greater relevance to natural contexts. We end by reporting exciting discoveries from recent studies of avian sibling recognition that inspire further interest in this topic. [source] Methods for Disseminating Research Products and Increasing Evidence-Based Practice: Promises, Obstacles, and Future DirectionsCLINICAL PSYCHOLOGY: SCIENCE AND PRACTICE, Issue 4 2002Michael E. Addis Although several different rationales for psychotherapy dissemination research have been well articulated, the most effective means for bringing research products to clinical practice have yet to be determined. Two commonly proposed methods are the dissemination of empirically supported treatments and the dissemination of general evidence-based stances to clinical decision making. Obstacles to either approach include (a) practical constraints on practitioners' ability to use research products, (b) lack of research on process and outcome of both empirically supported treatments and existing services in different practice contexts, (c) lack of research on acceptability of research products to end users including practitioners, clients, and administrators, (d) lack of research on training in the integration of science and practice at the undergraduate, graduate, and postgraduate levels, (e) systemic economic contingencies that favor or punish evidence-based decision making, and (f) the tendency to construct dissemination as a hierarchical and unidirectional process of transmission from research to clinical practice. Each obstacle is considered in detail and followed by recommendations for ways to broaden the scope of dissemination efforts. [source] | |||||||||||||